United States        Air and Radiation       EPA420-R-01-015
          Environmental Protection                June 2001
vxEPA    Performing Onboard
          Diagnostic System
          Checks as Part of a
          Vehicle Inspection and
          Maintenance Program
                                 > Printed on Recycled Paper

                                                                           June 2001
     of a
                                 David Sosnowski
                                 Edward Gardetto
                   Transportation and Regional Programs Division
                       Office of Transportation and Air Quality
                       U.S. Environmental Protection Agency

   This technical report does not necessarily represent final EPA decisions or positions.
It is intended to present technical analysis of issues using data, that are currently available.
        The purpose in the release of such reports is to facilitate the exchange of
     technical information and to inform the public of technical developments which
       may form the basis for a final EPA decision, position, or regulatory action.

    Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and
                                Maintenance Program

                                      June 2001


       The Clean Air Act as amended in 1990 (CAA) requires the Environmental Protection
Agency (EPA) to set guidelines for states to follow in designing and  running vehicle inspection
and maintenance (I/M) programs.  As well as distinguishing between basic and enhanced I/M
programs, these guidelines must clarify how states are to meet other minimum design
requirements set by the CAA. One such requirement that applies to both basic and enhanced I/M
programs is the performance of Onboard Diagnostic (OBD) system checks as part of the
required, periodic inspection.

       On November 5, 1992,  EPA published the I/M rule to meet most of the above-referenced
CAA requirements. At the time the I/M rule was promulgated, however, federal OBD
certification standards had not been published. To address the CAA's OBD-I/M requirement,
EPA reserved sections in the 1992 rule, with the understanding that these reserved sections
would be amended at some future date.  Although the federal requirement to incorporate OBD
into new vehicles began with the 1994 model year (MY), manufacturers were allowed to request
waivers on vehicles for MY 1994-95, so full compliance was not required on all light-duty cars
and trucks sold in this country until MY 1996. On August 6, 1996, EPA published amendments
to the 1992 I/M rule establishing OBD-I/M requirements for I/M performance standards and I/M
State Implementation Plans (SIPs).  The 1996 amendments also specified data collection,
analysis, and summary reporting requirements for the OBD-I/M testing element; established
OBD test equipment requirements and the OBD test result reporting  format; and identified those
conditions that would result in an OBD-I/M pass, failure, or rejection. Lastly, the August 6, 1996
amendments revised 40 CFR part 85, subpart W to establish OBD-I/M as an official  performance
warranty short test under section 207(b) of the Act.

       At the time the original OBD-I/M requirements were established, it was not practical to
evaluate the real-world, in-use performance of OBD because the vehicles in question were still
too new and the number of those vehicles in need of repair were too few to make pilot testing
worthwhile.  Therefore, in 1998, EPA further  amended its OBD-I/M requirements to delay the
date by which I/M programs must begin OBD testing to no later than January 1, 2001.

       One of the primary reasons for delaying the deadline for beginning OBD-I/M testing was
to give EPA time to evaluate the OBD check as an I/M program element and to give  states time
to prepare for implementation.  In conducting its evaluation of OBD, however, EPA  found that
identifying and recruiting OBD-equipped vehicles in need of repair proved more difficult and
time-consuming than originally anticipated. As a result, EPA has only recently completed the
assessment of OBD-I/M effectiveness and implementation issues referenced in this guidance.

During the course of this evaluation, however, it became clear that certain regulatory changes
were needed to ensure the smooth implementation of OBD-I/M testing by the states.

       In response to its findings on OBD effectiveness and its study of the various
implementation issues associated with OBD-I/M testing, EPA has amended the OBD-I/M testing
requirements by publishing a final rulemaking (FRM) in the Federal Register on April 5, 20011.
The goal of these amendments is to update and streamline requirements and to remove regulatory
obstacles that may otherwise impede the effective implementation of OBD-I/M testing.  Among
other things, the revised requirements: 1) provide states several options for extending the current
deadline for mandatory implementation of the OBD-I/M inspection beyond January 1, 2001; 2)
clarify states' options regarding the integration of OBD-I/M checks into existing I/M networks;
3) revise and simplify the current list of Diagnostic Trouble Codes (DTCs) that constitute the
OBD-I/M failure criteria to include any DTC that leads to the dashboard Malfunction Indicator
Light (MIL) being commanded on; and 4) provide for exemptions from specific readiness code
rejection criteria on OBD-equipped vehicles based upon vehicle model year.

       In addition to the above cited regulatory revisions, EPA believes it is important to
respond to states' requests to provide additional guidance  on how to successfully implement
OBD-I/M testing in an I/M program.  EPA is therefore issuing this guidance at this time in
response to those requests and to assist those states and local areas that are considering or
planning early implementation of OBD checks as part of their I/M programs.
Scope of Guidance

       This guidance incorporates several key recommendations made to EPA by the OBD
Workgroup, which is part of the Mobile Source Technical Review Committee, established under
the Federal Advisory Committee Act (FACA).  This guidance was also developed by drawing
from the experiences of several states that are currently performing some form of OBD-based
inspection. As of this writing, ten states (New York, California2, Colorado, Alaska, Illinois,
Wisconsin, Vermont, Oregon, Maine, and Utah3) are performing some form of vehicle OBD
system check and at least three other states (Indiana, New Hampshire, and Georgia) are actively
moving towards early implementation of vehicle OBD system checks. Lastly, the development
of this guidance was aided by comments received from stakeholders in response to an earlier,
draft guidance released for public comment in December 2000.
        Copies of the FRM are available via the Internet at www. epa. go v/oms/epg/regs.htm.

        Currently, California and New York are performing only a visual check for MIL illumination. A scanner check for
trouble codes will be added in the future.

        In Utah, the I/M program is administered at the county level (as opposed to at the state level). Although there are
several counties in Utah currently required to implement I/M, only one county - Davis - has opted to begin early implementation
of the OBD-I/M check.

       This guidance reflects EPA's current understanding of the challenges and issues unique to
the performance of OBD testing in the I/M program environment, and includes our
recommendations for how best to address those issues at this time.  As is the case with any
technology-driven pollution control measure, our understanding of the issues and the issues
themselves are likely to change over time as we gain more experience with them. Therefore,
EPA will update this guidance from time to time, as developments warrant. To ensure that this
document is updated accurately, EPA invites those involved with performing the OBD-I/M check
to share information with us by contacting Ed Gardetto at 734-214-4322, or via e-mail at
gardetto.edward@epa.gov. Program data, recommendations,  and other forms of feedback
relevant to the performance of the OBD-I/M check can also be sent to:

       Ed Gardetto c/o
       U.S. Environmental Protection Agency
       2000 Traverwood Drive
       Ann Arbor, MI 48105

       Lastly, this guidance does not  address those I/M implementation issues which are
common to all test types and for which there are no unique, OBD-specific considerations.  For
example, this  guidance does not address geographic coverage requirements or the adequacy of
program funding mechanisms. Readers can find EPA's requirements and/or recommendations
for these generic I/M implementation  issues by consulting the I/M rule (as amended) and EPA's
subsequent I/M policy documents, which are available via the Office of Transportation and Air
Quality (OTAQ) web site at: http:\\www.epa.gov\otaq\im.htm.
Vehicle OBD System Checks: Basic Requirements

Recommended Model Year Coverage

       Although some variety of OBD system has been an option on certain vehicle models
since the early 1980's, standardized OBD systems (also known as OBD II) were not introduced
until MY 1994, and such systems did not appear on all new light-duty vehicles sold in this
country until MY 1996. Therefore, for I/M purposes, EPA does not require that pre-1996 MY
vehicles be subject to the OBD inspection discussed in this guidance.  Furthermore, EPA does
not recommend that such testing include MY 1994-95 vehicles because not all such vehicles are
OBD-equipped and the availability to manufacturers of limited waivers from some OBD
requirements makes determining which of these vehicles to test (and to what standards)
administratively very difficult.  Additionally, EPA's MOBILE6 emission factor model will not
provide emission reduction credit for the performance of OBD-I/M checks on pre-1996 MY

       EPA also does not recommend that vehicles older than MY 1994 be subjected to OBD-
based I/M testing, even if it is determined that the vehicle is equipped with an OBD computer,

and may even have a malfunction indicator light (MIL) illuminated.  The reason we do not
recommend performing an OBD-I/M scan on pre-1994 MY OBD-equipped vehicles is because
such vehicles use an earlier, non-standardized generation of OBD system (also known as OBD I).
Due to the lack of federal standards for OBD I systems, the systems themselves tend to be
proprietary and may not be compatible with the  standardized OBD II scanners that will be used in
most I/M programs4.
Elements of an OBD-I/M Check

       An OBD-I/M check consists of two types of examination: A visual check of the
dashboard display function and status (also known as the MIL and/or bulb check) and an
electronic examination of the OBD computer itself.  These two examinations, taken together,
comprise the seven step procedure outlined below.

       1)     Initiate an official test by scanning or manually inputting the required vehicle and
              owner information into the reporting medium (i.e., PC-based electronic reporting
              system or manual test report).

       2)     Visually examine the instrument panel to determine if the MIL illuminates briefly
              when the ignition key is turned to the "key on, engine off' (KOEO) position.  A
              brief period of illumination of the MIL at start-up is normal and helps confirm the
              bulb is in proper, operating condition. This portion of the test procedure is also
              known as the "bulb check." Enter the results of the bulb check into the reporting

       3)     Locate the vehicle's data link connector (DLC) and plug a scan tool into the
              connector.  While it is recommended that this step be performed with the ignition
              in the "off position, this step can also be performed with the ignition running.
              Given the variety of locations manufacturers have chosen in practice, locating the
              DLC may well be the most time-consuming element of the inspection.  We will
              discuss the issue of atypical DLC location elsewhere in this guidance.

       4)     Start the vehicle's engine so that the vehicle is in the "key on, engine running"
              (KOER) condition5. The MIL may illuminate and then extinguish during this
              phase.  Continued illumination while the engine is running is cause for failure.
        40 CFR 85.2222 "On-board diagnostic test procedures" requires that the scan tool used for the OBD-I/M inspection
be capable of communicating with the OBD system in compliance with the Society of Automotive Engineers (SAE)
Recommended Practice J1979.

        While it is possible to perform the electronic scan portion of the OBD-I/M check in the KOEO position for most
vehicles, EPA discourages this practice because it can lead to false failures for some makes and models of vehicles (such as MY
1996-2001 Subarus).

               Also, if the MIL illuminates during this phase but was not observed in step 2, the
               vehicle should not be failed for step 2.

        5)     With the scan tool in the "generic OBD" mode, follow the scan tool
               manufacturer's instructions6 to determine:

                      Vehicle readiness status7

                      MIL status (whether commanded on or off)8, and

                      Diagnostic Trouble Codes (DTCs) for those vehicles with MILs
                       commanded on9.

        6)     Record the results of the OBD inspection in the appropriate medium. Depending
               upon the design and feature requirements of the program, this may be an
               automated process.

        7)     Without clearing DTCs or readiness codes, turn off the vehicle ignition, and then
               disconnect the scan tool10.  Clearing codes - if such is necessary - should be
               reserved for the repair portion of the program (even though in test-and-repair
               programs, the same personnel may be engaged in both activities). These codes
               (and the associated "freeze-frame" data) are important for the performance of
               proper diagnostics prior to repair.

        Although the above inspection elements  are listed sequentially, current regulations do not
specify the sequence that must be followed in performing the OBD-I/M inspection, and EPA sees
no reason for applying a rigid sequence at this time. In some cases it may make more  sense to
         For I/M purposes, the inspectors and repair technicians should be advised to conduct the scan in "generic" mode as
opposed to a vehicle manufacturer specific mode. EPA is aware of some instances in which using a scan tool in the vehicle
manufacturer specific mode will result in confusing or misleading readings regarding vehicle readiness.

        7 Refer to SAE J1979 MODE 01 PID 01 DATA C and D.

        8 Refer to SAE J1979 MODE 01 PID 01 DATA A BIT 7.

         EPA's original OBD-I/M failure criteria were limited to power-train, emission-related DTCs (refer to SAE J1979
MODE 03). In its April 5, 2001 rulemaking, however, EPA simplified the failure-triggering DTC criteria to any DTC that leads
to the MIL being commanded on.  As part of its technical support efforts for the April 5, 2001 rulemaking, EPA looked at six
months' worth of OBD-I/M data from the Wisconsin I/M program and found that less than 0.5% of the OBD-equipped vehicles
tested during that period experienced MILs being commanded on for DTCs falling outside the previous failure criteria. As a
result, EPA does not believe the simplified failure criteria will result in higher overall I/M failure rates  especially not in those
areas that opt to replace existing tailpipe testing on MY 1996 and newer vehicles with the OBD-I/M scan.

          For programs conducting both OBD and tailpipe testing on OBD-equipped vehicles, the tailpipe test may be
conducted prior to this step, to avoid an extra, unnecessary key-off, key-on cycle.

conduct the visual portion of the inspection after performing the onboard computer scan. For
example, a state choosing to perform both a traditional tailpipe test and the OBD-I/M check on
OBD-equipped vehicles may choose to reduce the overall test time involved by conducting the
OBD scan at the same time the other test is performed.  EPA has found that a scan tool can be
plugged into a still-running vehicle without producing erroneous readings.  Therefore, we believe
states should be allowed the flexibility to determine the optimum test sequence to meet their
programmatic needs.  However, EPA does caution that unforeseen problems may arise with some
subset of the fleet due to changes in the sequence.  EPA therefore asks that states consult with the
Agency should they find unusual failure patterns among certain makes and models of vehicles in
conjunction with the use of alternative test sequences.

        For readers who prefer their information presented graphically, a flowchart of an
acceptable OBD system check is included in Appendix E of this guidance document. It was
developed by the  Center for Automotive Science and Technology at Weber State University, and
is consistent with EPA guidance.
Basis for Failure or Rejection

       Unless otherwise noted in this guidance, a vehicle should be failed for any of the
following five reasons, with the exception of the last (for which the appropriate action is

       1)      It is a 1996 or newer vehicle and the data link connector (DLC) is missing, has
               been tampered12 with, or is otherwise inoperable.  (Action: Failure)

       2)      The MIL does not illuminate at all when the ignition key is turned to the KOEO
               position. The MIL should illuminate (on some vehicles, only for a brief period of
               time) when the ignition key is turned to the KOEO position. (Action: Failure)

       3)      If the MIL illuminates continuously or flashes  after the engine has been started,
               even if no fault codes are present, since this could indicate a serial data link
         States should be aware that some vehicles have atypical OBD configurations, and should take steps to avoid unfairly
penalizing motorists. For example, states may incorrectly suspect motorist tampering for those vehicles that are manufactured
with the DLC in a hard-to-find location.  EPA is working with manufacturers, operating OBD-I/M programs, and Weber State
University to develop an online clearinghouse of OBD-related information useful to state I/M programs and other stakeholders,
including all OBD-related Technical Service Bulletins (TSBs) from the manufacturers and all relevant updates. See Appendices
B through D for more information on vehicles with atypical OBD system issues.

         Tampering is considered to be any modification of the vehicle that deviates from the certified configuration of the
vehicle, particularly if such modification has the practical effect of making the vehicle untestable (by, for example, making the
DLC inaccessible) or otherwise constitutes an attempt to evade the program (by, for example, using illegal aftermarket devices
designed to circumvent the OBD computer or provide false results during an OBD-I/M check). Under this definition, moving a
DLC as part of collision repairs would not necessarily constitute tampering  provided the DLC was not hidden or rendered
otherwise inaccessible as a result of being moved.

               failure.13 (Action: Failure)
        4)     Any DTCs are present and the MIL status, as indicated by the scan tool, is
               commanded on. regardless of whether or not the MIL is actually illuminated.
               Do not fail the vehicle if DTCs are present and the MIL status, as indicated by
               the scan tool, is off, because such non-MIL-triggering DTCs are considered
               "pending" and frequently self clear without requiring repair of the vehicle.  MIL
               command status must be determined with the engine running.  (Action: Failure)

        5)     The number of OBD  system monitors showing a "not ready" status exceeds the
               number allowed for the model year in question. (Action:  Rejection)14

        Table 1 below lists the possible test outcomes in tabular form.

                             Table 1  - Possible OBD-I/M Outcomes
 Vehicle Passes If:
* Bulb check OK and
* MIL not lit while engine running and
* MIL not commanded on for any DTCs and
* All required readiness codes are set
 Vehicle Fails If:
  Bulb check not OK and/or
  MIL lit while engine running and/or
  MIL commanded on for any DTC and/or
  DLC missing, tampered, or inoperable
 Vehicle Rejected If:
  More unset readiness codes found than allowed based on MY and/or
  DLC cannot be located or is inaccessible
          States should be aware that some vehicles will illuminate a MIL when a scan tool is connected and the vehicle is still
in the "key on, engine off condition. In some cases, the scan tool will indicate that the MIL is, in fact, commanded on  even
though no DTCs may be present. EPA has found that these vehicles will usually extinguish the MIL and remove the "MIL
commanded on" indicator when the engine is started. To avoid falsely failing vehicles, therefore, it is important that the
electronic portion of the OBD-I/M check be conducted only with the vehicle in the "key on, engine running" condition (as
indicated in the test procedure described above).

         Although earlier requirements stipulated that OBD-equipped vehicles be rejected from further testing if any  monitor
was "not ready," EPA has revised these readiness criteria to allow states to not reject MY 1996-2000 vehicles with two or fewer
unset readiness codes, or MY 2001 and newer vehicles with no more than one unset readiness code. The complete MIL check
and scan should still be run in all cases, however, and the vehicle should still be failed if one or more DTCs are set and the MIL
is commanded on. The vehicle should also continue to be rejected if the OBD computer does not set readiness codes for 3 or
more monitors on MY 1996-2000 vehicles, or two or more monitors on MY 2001 and newer vehicles.  Readiness codes in
general, and the specific codes and conditions covered by the April 5, 2001 amendments will be discussed in more detail under a
separate section of this guidance.

I/M-Related DTCs

       Until recently, Federal I/M regulations identified a subset of power train (or P-code)
DTCs as being relevant for I/M purposes. If a vehicle was identified through an I/M program as
having a MIL commanded on for one or more of those P-codes, then Federal regulations
required that the vehicle fail the inspection. In an attempt to simplify these failure criteria - and
to harmonize Federal requirements with California Air Resources Board (CARB) requirements
- EPA amended this requirement as part of its April 5, 2001 rulemaking. Under the revised
failure criteria, a vehicle shall now be failed for the presence of any DTC that results in the
"Check Engine" MIL being commanded on.

       In commenting on an earlier draft of this implementation guidance, several commenters
raised concerns that EPA's simplified failure criteria would result in vehicles being failed for
non-emission related components or systems, such as the brakes or suspension. Although some
vehicle onboard computers may monitor non-emission-related components and systems at the
manufacturer's  discretion, Federal regulations require that the "Check Engine" MIL only be
illuminated for emission-related malfunctions.  Other dashboard lights may be illuminated to
indicate the need for service of a non-emission-related component or  system, but the presence
of such lights does not constitute grounds for failing the OBD-I/M check.  Furthermore, EPA
has examined data from over 300,000 OBD-I/M checks performed in actual I/M lanes and has
not found a single instance of the simplified failure criteria leading to the failure of a vehicle for
a non-emission-related component or system.

       EPA also wants to acknowledge that it is possible we may need to limit the criteria for
failing OBD-equipped vehicles after such vehicles reach an as-yet undetermined age and/or
mileage. The reason for considering this possibility stems from the fundamental difference
between how OBD triggers repairs versus how traditional tailpipe tests trigger repairs.
Traditional I/M tailpipe tests identify a vehicle as failing for a given pollutant through direct
sampling of the exhaust plume. These tests vary in the degree to which they provide any
additional information that can be used to target the component or system failure that has led to
the  high emission reading.  In such programs, repair technicians have a fair degree of discretion
when it comes to recommending repairs to address a given failure, although owners are
protected from excessive economic hardship by the cost waiver option. OBD, on the other
hand, identifies specific components and/or systems in need of repair or replacement.  As a
result, EPA foresees the possibility that some advanced-aged OBD-equipped vehicles could be
failed for DTCs for which the only available repair option would cost substantially more than
the  fair market value of the vehicle itself. Under such a scenario, the  waiver option does not
offer much consumer protection, since such repairs tend to be all-or-nothing propositions. For
example, a motorist faced with a transmission repair cannot reasonably opt to have the
transmission "half fixed" to take advantage of the cost waiver option.

       Given the relative newness of OBD II, EPA has not been able to gather the data

necessary to determine whether situations like the one above will actually happen in practice
(though the Agency certainly plans to gather such data in the future). We do believe however
that program requirements should be reasonable,  and that the economic burdens of a program
should be balanced by the environmental benefit  likely to result from the imposition of those
burdens.  Therefore, we may revise our failure criteria at some future date, once data has been
gathered  and analyzed concerning the actual costs associated with repairing high mileage/age
OBD-equipped vehicles across the full range of possible MIL-triggering DTCs.
Test Report

       If a vehicle fails, the test report given to the motorist should include the status of the
MIL illumination command and the alphanumeric fault code(s) listed along with the DTC
defmition(s) as specified per SAE J2012 and J1930.  Only the fault codes leading to the
inspection failure should be listed on the report given to the motorist. EPA makes this
recommendation because it is possible that an OBD system may set DTCs without commanding
a MIL to be illuminated. These DTCs usually reflect an intermittent condition which may or
may not be a problem at the time of testing. If the condition does not recur within a certain
number of trips, the code will eventually be cleared; if the condition does recur, the system may
then determine that a MIL should be illuminated.  Therefore, no DTCs should be printed on test
reports for vehicles that pass the inspection. An owner who receives notice of these codes on
the same sheet of paper with notification of passing the state inspection may become confused
or desensitized to the importance of DTCs and the MIL. Lastly, unset readiness codes should
also be listed on the report if the number of unset readiness codes exceeds the limit for which
an exemption is allowed (i.e., if the outcome of the test is rejection based upon the presence of
too many unset readiness codes). If the number of unset readiness codes falls below the limit
for which an exemption is allowed (and the vehicle would otherwise pass the inspection) then
no unset readiness codes should be listed on the test report provided to the motorist.
Readiness Status: Initial Test

       The OBD system monitors the status of up to 11 emission control related subsystems by
performing either continuous or periodic functional tests of specific components and vehicle
conditions. The first three testing categories - misfire, fuel trim, and comprehensive
components - are continuous, while the remaining eight only run after a certain set of
conditions has been met.  The algorithms for running these eight, periodic monitors are unique
to each manufacturer and involve such things  as ambient temperature as well as driving
conditions. Most vehicles will have at least five of the eight remaining monitors (catalyst,
evaporative system, oxygen sensor, heated oxygen sensor, and exhaust gas recirculation or EGR
system) while the remaining three (air conditioning, secondary air, and heated catalyst) are not
necessarily applicable to all vehicles. When a vehicle is scanned at an OBD-I/M test site, these
monitors can  appear as either "ready" (meaning the monitor in question has been evaluated),

"not ready" (meaning the monitor has not yet been evaluated), or "not applicable" (meaning the
vehicle is not equipped with the component monitor in question).

       There are several reasons why a vehicle may arrive for testing without the required
readiness codes set. These reasons include the following:

       1) Failure to operate the vehicle under the conditions necessary to evaluate the
          monitor(s) in question;

       2) A recent resetting of the OBD system due to battery disconnection or replacement,
          or routine maintenance immediately prior to testing15;

       3) A unique, vehicle-specific OBD system failure;

       4) An as-of-yet undefined system design anomaly; or

       5) A fraudulent attempt to avoid I/M program requirements by clearing OBD codes just
          prior to OBD-I/M testing (by, for example, temporarily disconnecting the battery).

       In addition to the above considerations, EPA has also found that a small number of
vehicles may be flagged as "not ready" or "not supported" for one or more of the continuous
monitors (i.e., misfire, fuel trim, and/or comprehensive components). This makes no sense
because continuous monitors are designed to run continuously (as their name implies) and
therefore should always be flagged as "ready."  In its investigation of this issue, EPA has
determined that the problem is the result of incompatibility between the vehicle and scanner
software and is not indicative of a fault with the vehicle's OBD system. As a result of this
discovery, EPA recommends that programs disregard these continuous monitors when
establishing the readiness status of the vehicle.  This exclusion is for readiness determination
purposes only: a vehicle with a MIL commanded on for a continuous  monitor based DTC
should continue to be failed in compliance with the test procedure discussed earlier in this
guidance. EPA is working with state programs and OBD software suppliers to address this
issue and will issue revised guidance as warranted.

       Because the presence of unset readiness codes among the non-continuous monitors
could be a sign of attempted fraud, it is important that all OBD-equipped vehicles be checked to
confirm that readiness codes have been set as one of the pre-requisites for a valid OBD-I/M
inspection. Nevertheless, as described in the FRM, EPA also believes that the previous
requirement regarding readiness codes (i.e., that a vehicle be rejected from further testing if any
monitor is found to be "not ready") was more rigorous than either necessary or practical.
Therefore, as discussed under "Basis for Failure or Rejection" above, EPA has revised the
         As part of a program's outreach effort, car owners should be advised to allow for approximately one week of normal
vehicle operation after repairs and prior to OBD-I/M testing (or retesting).


readiness requirement so as to allow states to complete the testing process on MY 1996-2000
vehicles with two or fewer unset readiness codes; for MY 2001 and newer vehicles, the testing
process can still be completed provided there is no more than one unset readiness code.  This
does not mean that these vehicles are exempt from the OBD-I/M check16.  The complete MIL
check and scan must be run in all cases, and the vehicle still must be failed if any of the failure
criteria discussed in this guidance are met.  The vehicle should continue to be rejected if it is
MY 1996-2000 and has three or more unset, non-continuous readiness codes or is MY 2001 or
newer and has two or more unset, non-continuous readiness codes.

       As discussed in the Technical Support Document for the FRM, this amendment is based
upon EPA's findings regarding readiness codes from Wisconsin's OBD-I/M data and also
reflects a FACA workgroup recommendation. Since August 1998, Wisconsin's I/M program
contractor has been sending to EPA OBD scanning and EVI240 test results data collected on
MY 1996 and newer vehicles coming through the Wisconsin I/M test lanes.  In analyzing the
Wisconsin data, EPA made the following observations regarding the readiness status of the
OBD-equipped vehicles presented for testing17:

          The majority of vehicles showing up at the I/M lane with readiness codes reading
           "not ready" were from MY  1996; the "not ready" rate for MY 1996 vehicles was

          The frequency of vehicles with readiness codes reading "not ready" dropped off with
           each successive model year -  to 2.2% for MY 1997 and  1.4% for MY 1998.

          If an exemption were allowed for up to two readiness codes to read "not ready"
           before a vehicle would be rejected from further testing, the rejection rate drops - to
           2.2% for MY 1996 and to 0.2% for MY 1997 and MY 1998, for  a three model year
           average of 0.9%.

       The intention behind EPA's decision to allow limited exemptions from the readiness
         As discussed above, when determining the readiness status of a vehicle, EPA recommends that programs only
consider the non-continuous monitors. Likewise, in assessing whether a "not ready" vehicle can be exempt from the readiness
rejection requirement based upon the number of unset readiness codes present, only unset readiness codes among the non-
continuous monitors should be counted.

         In commenting on an earlier draft of this implementation guidance, some commenters suggested that EPA's figures
regarding the frequency of "not ready" vehicles in the in-use fleet are skewed downward because the Agency's data comes from a
program where the OBD-I/M check is being performed on an "advisory only" basis.  These commenters argued that in an
"advisory only" program motorists had no incentive to fraudulently clear MILs by disconnecting the battery since there was no
negative repercussion from showing up for the inspection with a lit MIL.  These commenters further argued that once motorists
began failing based upon MILs, the frequency of vehicles with unset readiness codes at the time of the initial test would go up.
To test this hypothesis, EPA has begun analyzing program data from the Oregon OBD-I/M program, which is currently failing
vehicles based upon the results of the OBD-I/M check. Based upon a preliminary analysis of the Oregon data, EPA has found
that roughly 1.4% ofMY1996+ vehicles are being rejected at the time of the initial test due to an excessive number of "not
ready" codes (assuming the readiness exemption allowance provided by the April 5, 2001 FRM).


rejection criteria is exclusively to avoid inconveniencing motorists on the basis of vehicle
conditions that are beyond their control, that are currently the subject of discussion between
EPA and various manufacturers, and that, in some cases, may result in potential enforcement
action.  The purpose of the limited readiness exemption is not to relieve manufacturers of their
responsibility to design and market OBD systems that comply with existing OBD certification
requirements18.   Nothing in this guidance in any way changes or otherwise impacts these
obligations on the part of vehicle  manufacturers. In fact, EPA has already initiated  several
investigations which may result in enforcement actions related to these requirements.

       Because of the small number of vehicles involved, EPA believes that the environmental
impact of the limited readiness exemption will be negligible, especially given the likelihood
that at least some of these readiness codes will have been set in  time for subsequent OBD-I/M
checks, and the fact that an unset  readiness code is not itself an  indication of an emission
problem.  EPA believes that allowing limited exemptions from the readiness code requirement
as described above makes the most sense at this time, while EPA, CARB, and the
manufacturers work to clarify  system function requirements with regard to I/M.  Lastly, EPA
does not believe that allowing these limited exemptions will interfere with the use of readiness
codes to help deter possible fraud because such fraud would inevitably lead to more monitors
being set to "not ready" than are allowed under EPA's limited exemptions.

       In addition to the above exemptions, EPA also recommends that I/M programs waive
the readiness requirement or otherwise accommodate specific makes, models, and model years
of vehicles with known readiness design problems, in  accordance with applicable technical
service bulletins and/or EPA guidance.  EPA has compiled a list of such vehicles and included
it in Appendix D.

       Even with these vehicle-specific accommodations and the above exemptions, however,
some vehicles will still need to be rejected based upon readiness code status.  In the case of a
vehicle rejected for unset readiness codes (which does not otherwise meet the failure criteria
described in this guidance), the motorist should be given the option of operating the vehicle for
a week under normal operating conditions in an attempt to evaluate the necessary monitors
without being required to visit a repair facility prior to retesting. If the monitors still have not
performed an evaluation by the first retest, the motorist should then be advised to visit a repair
       1 8
         To help emphasize this point, EPA clarifies here that the obligations of the automobile manufacturers with regard to
OBD equipment are specified in regulatory section 40 CFR 86.094-17(e)(l): "Control of Air Pollution From New Motor
Vehicles and New Motor Vehicle Engines: Regulations Requiring On-Board Diagnostic Systems on 1994 and Later Model Year
Light-Duty Vehicles and Light-Duty Trucks," which imposes, among other things, the obligation to design, build and certify
OBD systems that: "record code(s) indicating the status of the emission control system. Absent the presence of any fault codes,
separate status codes shall be used to identify correctly functioning emission control systems and those emission control systems
which need further vehicle operation to be fully evaluated." In promulgating these requirements on February 19, 1993 the
Agency stated: "The readiness code will ensure I/M testing personnel and service technicians that malfunction codes have not
been cleared since the last OBD check of the vehicle's emission-related control systems. This code will be essential... since I/M
personnel must be sure that the OBD system has sufficient time to completely check all components and systems. The readiness
code is also crucial for indicating to service personnel whether any repairs have been conducted properly."


facility where the monitors can be set based upon vehicle-specific, manufacturer guidance.
Alternatively, states may decide to allow such vehicles to default back to the traditional I/M
tests performed on the vehicles in question prior to introduction of the OBD-I/M test
requirement.  EPA recommends that states that choose to use back-up tailpipe testing in lieu of
rejection track this activity carefully to ensure that the practice does not lead to an inadvertent
loophole through which motorists routinely avoid the OBD-I/M inspection in favor of the
tailpipe test.

       In all cases, it is important to emphasize that lack of readiness is a special status
particular to OBD systems and that the vehicle is not necessarily producing excess emissions.
Instead, the vehicle's emissions status is officially "Unknown," due to a failure to meet
certain monitoring conditions prior to the inspection. In order to minimize confusion, EPA
recommends that states provide a written statement about OBD and readiness status to
motorists who are rejected based upon an excessive number of unset  readiness codes.  Such a
statement should make the following key points:

       1) A vehicle rejected as "not ready" is not necessarily "dirty."

       2) "Not ready" just means the vehicle's computer has not had an opportunity to fully
          evaluate the vehicle's performance.

       3) Many circumstances can lead to a vehicle being "not ready," including recent
          vehicle repairs  and/or battery replacement.

       4) In most cases, a week's worth of continued  vehicle operation under normal
          operating conditions will be sufficient to make a "not ready" vehicle "ready."

       5) In a very limited number of cases (less than 1%), a "not ready" vehicle may need
          to be taken to a repair facility, where the readiness codes can be  set based upon
          vehicle-specific, manufacturer guidance.
Readiness Status: Retest After Repairs  Non-catalyst-related DTCs

       OBD-I/M programs also must address the readiness code status of vehicles returning for
retesting after repairs have been performed to correct an initial OBD-I/M failure. Even if the
vehicle showed all readiness codes as "ready" on the initial test, vehicles returning to the I/M
lane immediately following repair will likely have just had the fault code memory cleared by
the repair technician (the proper step following a repair). Upon clearing the fault code memory,
however, all readiness codes will also be cleared and set to "not ready."  If the vehicle returns
for retesting immediately after repair, it is possible that one or more readiness codes will
register as "not ready." To address this possibility, EPA recommends that the vehicle be held to
the same readiness criteria as are applicable for an initial test (i.e., if the vehicle is MY 1996-

2000, a maximum of any two unset readiness codes may be allowed, while for MY 2001 and
newer vehicles, no more than one unset readiness code is allowed).

       To help minimize the potential for vehicles showing up for their retest with an excessive
number of unset readiness codes, outreach to the repair community should stress the importance
of confirming vehicle readiness prior to returning a repaired, OBD-equipped vehicle to its
owner.  Motorists should also be informed that they should plan to allow a week's worth of
ordinary driving between receiving repairs and getting a vehicle retested, to avoid being
rejected based upon an excessive number of unset readiness codes.  If, despite these caveats, a
vehicle is presented for retesting with an  excessive number of unset readiness codes after repair,
EPA believes that the submission of repair receipts as proof of repair is an adequate method for
establishing that the necessary repairs have been performed. EPA appreciates that the ability of
inspectors to confirm repairs prior to retesting will vary, depending upon whether the I/M
program is a test-and-repair or test-only program. In the case of test-only programs, outreach
efforts to the repair community should stress the importance of including an indication on the
repair receipt that the repairs in question  are OBD-related (i.e., by including the diagnostic scan
in an itemized list of services performed). A repair receipt (as opposed to a repair estimate)
including evidence of a diagnostic scan and dated either on the same day as the initial test or
sometime thereafter may be considered adequate for establishing proof-of-repair for retest
purposes in test-only programs.  In the case of owner-performed repairs, the program should
require the submission of appropriately dated parts receipts prior to  retesting, and these receipts
should be reviewed by the test station manager, who in turn should be trained to determine
whether the parts in question are relevant to the cause of failure.  EPA believes that the number
of vehicles falling into this last category (i.e., OBD-equipped vehicles that fail  the initial test
and return for retesting with owner-performed repairs and an  excessive number of unset
readiness  codes) should be relatively small19.

       In commenting on an earlier draft of this implementation guidance, some commenters
raised concern that it would be possible for repair technicians to selectively clear DTCs without
performing repairs and without setting the remaining monitors (i.e.,  those without DTCs
recorded) to "not ready." If this were possible  the commenters argued  then vehicles that
should be failed could be fraudulently passed on the retest (even without receiving repairs)
because of the readiness exemptions allowed by EPA (assuming the number of DTCs resulting
in the initial failure did not exceed the number of readiness exemptions allowed for the model
year in question).  In reality, it is not possible to selectively clear DTCs or to only set some
readiness  monitors to "not ready" while leaving the remaining monitors "ready."  As  currently
designed,  the feature which allows the clearing of DTCs is an all-or-nothing proposition 
         In looking at data from the Oregon OBD-I/M program, EPA has found that for the tailpipe test, the average number
of retests required before passing after the initial failure is 2.01, while for vehicles failing the OBD-I/M check, the average
number of retests required before passing after the initial failure is 1.39 (even after accounting for the retest rejection rate
associated with the readiness issue described in this section).


specifically to avoid fraud such as that suggested by the commenters20.
Readiness Status: Retest After Repairs - Catalyst-related DTCs (P0420 - P0439}

       Based upon an analysis of data from the Oregon OBD-I/M program EPA recommends
that vehicles which fail the initial OBD test for any of the catalyst monitoring codes (P0420
through P0439) be held to a higher standard for the retest than is the case with other failure
codes. EPA recommends that initial catalyst failures follow one of the following steps at the
time of retest:

       1) If the catalyst  monitor is "ready" at the time of retest, then the vehicle should be
          treated like any other vehicle returning for retest after failing for any non-catalyst-
          related DTC.

       2) If the catalyst  monitor is "not ready" at the time of retest, then the owner should be
          required to provide proof of repair, or the vehicle should be required to pass a
          tailpipe test to verify catalyst function.

       3) Alternatively,  at the program's discretion, if the catalyst monitor is "not ready" at
          the time of retest, the vehicle should be rejected until the catalyst monitor has been
          set to "ready."
Readiness Status: Continuous Monitors

       As previously mentioned, EPA has found that a small number of vehicles may be
flagged as "not ready" or "not supported" for one or more of the continuous monitors (i.e.,
misfire, fuel trim, and/or comprehensive components).  EPA recommends that programs
exclude these continuous monitors from consideration when establishing the initial readiness
status of the vehicle. This exclusion is for readiness determination purposes only: a vehicle
with a MIL commanded on for continuous monitor based DTCs should continue to be failed in
compliance with the test procedure discussed earlier in this guidance. EPA is working with
state programs and OBD software suppliers to address this issue and will provide revised
guidance as warranted.

       In the case of vehicles which fail the initial OBD-I/M check exclusively for DTCs
related to the continuous monitors, repair technicians should be instructed to not clear the DTCs
electronically after performing the necessary repairs.  Instead, the success of repairs based upon
continuous monitor related DTCs should be confirmed by letting the OBD system detect the
repair and reset itself to "ready" (a process which should occur naturally after 3 engine key-
       20 Refer to SAE J1979 - "E/E Diagnostic Test Modes," Mode $04.

on/key-off cycles, provided the repairs were performed correctly).  In the case of initial failures
for a mix of continuous and non-continuous monitor related DTCs, the DTCs should continue
to be cleared, post-repair, as recommended elsewhere in this guidance.
Evaporative System Testing and OBD

       EPA's analysis of the Wisconsin I/M lane data suggests that OBD-I/M testing can be
supplemented by including a separate gas-cap check.  When EPA compared failure rates for the
evaporative portion of the OBD-I/M test to the failure rate for the stand-alone gas cap test we
found that the separate gas cap test was able to identify a substantial number of leaking gas caps
that were not identified by the OBD monitors due to the different failure thresholds.

       The seeming disparity described above is a result of the different detection thresholds
for the two tests.  The stand-alone gas cap test was designed to detect a leak as small as 60
cubic centimeters per minute (cc/min) at a pressure of 30 inches of water, while OBD systems
were designed to detect leaks equal to a circular hole 0.040 inches in diameter. The 0.040 inch
hole equates to a flow rate in excess of 2,600 cc/min at 10 inches of water column (i.e., the
maximum allowable internal tank pressure using the enhanced evaporative emission test)21. As
a result, an OBD system can reliably detect a loose or missing gas cap, while a properly
tightened but leaking gas cap that can easily be identified by the gas cap test will probably not
be identified by OBD.

       Since the gas cap test is able to identify an excessive emission condition not identified
by OBD, EPA recommends including this additional testing element in those areas that need
substantial reductions in hydrocarbon (HC) emissions from mobile sources as part of their
ozone attainment plans. For states with more modest  air quality needs with regard to mobile
sources, EPA is leaving it to the states to assess their needs regarding whether or not gas cap
testing is added to the OBD testing regime.  EPA is reserving judgement at this time because
we still do not have sufficient data to draw reliable conclusions concerning the frequency of
leaking gas caps in the in-use fleet. Our efforts in these areas have been complicated as a result
of pre-inspection replacement of the gas cap and, in some cases, a failure by inspectors to
record the initial gas cap failure as a failure. During informal audits of such programs, EPA has
found that the faulty gas cap is frequently replaced on the spot, or the owner is directed to
simply replace the cap  later without being required to  return for a retest22.
         During its pilot testing of OBD evaporative monitor effectiveness, EPA found that some in-use OBD systems were
capable of detecting leaks from holes as small as 0.020 inches in diameter. A 0.020 inch hole equates to 600 cc/min at 10 inches
of water column pressure.

         EPA encourages states conducting the gas cap pressure check to stress the importance of performing and recording
the results of the gas cap test accurately as part of their on-going outreach, training, and enforcement activities.


Implementation Issues for Centralized vs. Decentralized OBD-Based Testing

       While EPA recommends that I/M programs integrate OBD-I/M test procedures into
an overall, PC-based, real-time data-linked testing system, we understand that some programs
which do not currently require test stations to be linked to a real-time database may opt to use
generic, stand-alone, handheld scanners that do not generate automatic test reports and are
not tied to a real-time data-linked system.  While the use of stand-alone scanners is not barred
by I/M regulations for those areas not otherwise required to employ a real-time database,
EPA nevertheless sees several drawbacks to the stand-alone approach to OBD-I/M testing.
For example, the lack of a real-time data link will mean that program oversight will
necessarily be more costly, more labor intensive, and also less comprehensive, leaving the
program perhaps more vulnerable to fraud. This decrease in program  oversight effectiveness
would come at a time when a significant portion of the program itself is reverting to what is,
in effect, a manual test program, where test reports are filled out by hand from information
read off a handheld scanner's screen. Historically, programs that rely  upon a non-automated
process for making pass/fail decisions have been found to be even more difficult to oversee
than traditional decentralized programs, since no electronic record is produced, making
auditing more difficult. Furthermore, the use of computer matching to identify non-
complying vehicles would be seriously restricted under such a system, assuming that such a
system would not result in an electronically searchable testing database. And while it is
possible that manually-completed test reports could be made computer-scannable and
collected during site visits or sent to the state, the inherent time lag between the test and
inclusion in the state database makes this a challenging implementation issue (i.e., a negative
hit could equal data lag, not necessarily non-compliance). Lastly, the  individual station's
access to extensive and important program information (for example, DLC location databases
and technical service bulletins regarding program updates, pattern failures, etc.) would be
limited, both in terms of availability and timeliness.

       At a minimum, EPA believes that for an OBD-I/M test program to be most effective -
- whether centralized or decentralized  it should be designed in such a way as to allow  for:

          Real-time data link connection to a centralized testing database;

          Quality-controlled input of vehicle and owner identification information
          (preferably automated, for example, through the use of bar code); and

          Automated generation of test reports.
OBD and Inspector Fraud

       As is the case with all other I/M test types, the OBD-I/M check is vulnerable to
inspector fraud, and program managers need to be on guard to limit the opportunities for this

kind of activity.  For example, it is currently possible for an unscrupulous inspector in a
tailpipe-based program to engage in a practice known as "clean piping," where a known-
clean vehicle is tested while the vehicle identification information for another (presumably
dirty) vehicle is entered into the test record.  Similarly, there is a limited opportunity for an
inspector to "clean scan" an OBD-equipped vehicle, but there are also methods for keeping
this type of activity in check. The opportunity for "clean scanning" exists because the vehicle
identification number (VIN) is not currently included in the data stored in the vehicle's
onboard computer. Unlike "clean piping," however (where almost any known-clean vehicle
will do), the opportunity for large-scale "clean scanning" can be greatly reduced through the
use of identity-limiting information which is currently available from the vehicle's OBD
system. For example, programs could tally the number of Parameter Identifications (PIDs)23
supported by the vehicle, which can be used as a check against the other vehicle information
entered into the test record.  Another important number to capture and track for quality
control purposes is the Powertrain Control Module (PCM) diagnostic address24. While these
numbers do not identify a vehicle down to the level of an individual registration and owner,
they do allow for the separation of vehicles into different makes, models, and engine families.
Put another way, the PID count and PCM diagnostic address for a Honda Accord will be
different from that of a Ford Escort.  Therefore, programs can limit the potential for fraud via
"clean  scanning" by comparing the PID count and/or the PCM diagnostic address to the other
vehicle information in the test record. EPA is working with manufacturers and states
currently implementing the OBD-I/M inspection to gather the data necessary to interpret PID
count and PCM diagnostic address information so it can be used for this purpose.

       In commenting  on an earlier draft of this implementation guidance,  some commenters
suggested that even though the use of PID counts and PCM diagnostic addresses could limit
the potential for fraud via "clean scanning" among garages and service stations, it does not
pose much  of a deterrent for dealerships, which have a readily available supply of vehicles of
the same make and model as vehicles being tested. While this may be the case, EPA does not
believe that the potential for fraud among OBD-equipped vehicles is any higher than the
current potential for fraud via clean piping. Furthermore, if a state is concerned that
dealerships pose a greater fraud threat than other service providers, the state certainly has the
discretion to monitor the compliance of those dealerships and take appropriate enforcement
action, should fraud be detected.
Repair Cost Waivers and OBD

       Though for equity reasons it may be difficult for states to eliminate the waiver option
for OBD-tested vehicles, EPA recommends that states consider at least modifying waiver
       23 Refer to SAE J1979 MODE 01 PID 00.
       24 Refer to SAE J1979 Section 4.2.4 Header Bytes.

requirements for such vehicles.  The reason for wanting to avoid granting a waiver to a
vehicle with an illuminated MIL is two-fold: 1) it reinforces bad behavior (i.e., ignoring
illuminated MILs) and 2) once lit, a MIL that was illuminated for a relatively minor problem
effectively eclipses new, major problems, should they develop.  At a minimum, the state's
public education efforts regarding the OBD inspection should stress the importance of
responding to illuminated MILs in a timely manner.
Public Outreach

       In recognition of the pivotal role repair technicians and the public play in the success
of I/M programs, EPA recommends that all states required to perform vehicle OBD system
checks begin public outreach and technician training six months to a year prior to the
beginning of mandatory OBD testing25.  Therefore, another reason for issuing this guidance at
this time is to give states the opportunity to consider the various issues raised by and
addressed in this guidance in the development of their public outreach and technician training
efforts.  The need for public outreach is also one of the reasons EPA has provided states
several options for postponing the deadline for mandatory OBD testing beyond January 1,
2001 as part of its April 5, 2001 rulemaking.

       To facilitate a smooth incorporation of OBD-based testing of OBD-equipped vehicles
into I/M programs states should not underestimate the importance of effective public
outreach campaigns to inform motorists and the repair community about OBD and how it
works, what the MIL is and how to respond to it, and the environmental and consumer
benefits of OBD.  Thorough explanation of the OBD system within the context of I/M testing
may guard against the negative public perception which accompanied the introduction of
loaded mode testing in many areas. Extra care may need to be taken in areas where loaded
mode testing made the state emissions testing a "hot button" issue.

       Once developed, public educational materials should be disseminated as widely as
possible.  Relevant distribution points include: Trade organizations, dealerships (service
writers as well as technicians), AAA and other insurance-provider newsletters, private
garages, owners manuals for MY 1996 and newer vehicles, EPA publications, auto shows,
drive-time radio advertisements, automotive magazines, and environmental public service
announcements.  In pursuing their public outreach efforts, states should be sure to involve all
relevant parties in the process of developing and distributing materials.  These include:  State
         EPA also recommends that states consider factoring in a month or more of voluntary, advisory-only testing to allow
inspectors and motorists to get accustomed to the program and to allow for debugging prior to the beginning of mandatory testing
with mandatory repairs upon failure. Under such a scenario, a vehicle would be given a complete OBD-I/M test with the
exception that vehicles would not be failed on the basis of the OBD-I/M check alone, and would, instead, be issued an advisory
notice indicating that the vehicle is experiencing a problem for which it will be failed if corrective action is not taken prior to the
next test cycle.  Under the one-test-cycle phase-in option allowed by the April 5, 2001 FRM, vehicles which fail the OBD-I/M
check but pass the tailpipe inspection should be provided an advisory such as the one described above if they are excused from
being repaired during the phase-in period.


legislators, local leaders, automobile manufacturers, automobile enthusiasts, scan tool
manufacturers, EPA regional offices, emission inspection contractors, environmentalists,
health professionals, AAA and other automotive insurance providers, technical colleges,
service writers, private garages and repair chains.

Technician Training

       The success of a state's OBD-I/M effort will also depend on making sure that the
repair community is prepared to address the sorts of vehicles that are identified by the OBD
scan as needing service and/or repair.  States should work with their local educational
institutions, OBD equipment vendors, and other training providers to ensure that the
necessary training is available to repair technicians in the field well in advance of mandatory
OBD-I/M testing. In addition, states should also work with the various organizations
representing the repair community to stress the need for repair technicians to take advantage
of the training opportunities that are available.

       In I/M programs where repair technicians  are licensed or certified by the state to
participate in the program, OBD-specific repair technician training should be required as a
prerequisite to such licensing or certification. Such training should address the following
topics, at a minimum:

             The basics of OBD (i.e., theory, terminology, legal requirements, etc.)

              The differences between OBD I and OBD II

             The OBD-I/M inspection procedure

             The pass, fail, and rejection criteria for OBD-equipped vehicles

             Readiness, the setting and clearing of codes, and MIL-triggering vs. pending

             The link between the OBD-I/M check and the environment, and

             Proper diagnostic procedures and available sources of diagnostic materials
              (i.e., manufacturers, hotlines, web  sites, etc.).


                      Glossary of I/M- and OBD-Related Terms
Basic I/M: A vehicle inspection and maintenance program designed to meet the basic I/M
performance standard which includes performance of an idle test on 1968+ passenger cars.
Under the 1990 Amendments to the Clean Air Act, basic I/M is required in moderate
nonattainment areas, as well as those areas already implementing or required to implement a
basic I/M program prior to passage of the 1990 Amendments.

"Check Engine" Light: See the definition for Malfunction Indicator Light (MIL) below.

Diagnostic Trouble Codes (DTCs): An alphanumeric code which is set in a vehicle's onboard
computer when a monitor detects a condition likely to lead to (or has already produced) a
component or system failure, or otherwise contribute to exceeding emissions standards by 1.5
times the certification standard.

Enhanced I/M: A vehicle inspection and maintenance program designed to meet one of three
enhanced I/M performance standards - high, low,  and ozone transport region (OTR) low.
The high enhanced standard is designed around EVI240 tailpipe testing and purge and
pressure evaporative system testing. The low enhanced standard is similar to the basic I/M
performance standard, but includes light-duty trucks and a visual antitampering inspection.
The OTR low enhanced performance standard is designed for areas which would not be
required to do I/M at all, save for their location within the Northeast Ozone Transport
Region. The OTR low enhanced standard is based upon tailpipe testing using remote sensing
devices and visual antitampering inspections. Serious and worse nonattainment areas are
required to implement enhanced I/M, as well as all areas within the OTR with populations
over 100,000, regardless of attainment status.

Evaporative  System Test: A test of a vehicle's evaporative control system to determine if the
system is 1) leaking and/or 2) purging properly.

Malfunction Indicator Light (MIL): Also known as a Check Engine light, the Malfunction
Indicator Light of MIL is illuminated on the dashboard when conditions  exist likely to result
in emissions exceeding standards by 1.5 times or worse.  Alternatives include "Service
Engine Soon," as well as an unlabeled picture of an engine.

Onboard Diagnostics (OBD): A system of vehicle component and condition monitors
controlled by a central, onboard computer running software  designed to signal the motorist
when conditions exist which could lead to a vehicle's exceeding its emission standards by 1.5
times the standard.

OBD Data Link Connector (DLC): The interface - usually located under the dashboard on
the driver's side - between a vehicle's OBD computer and the OBD scanner. Connecting an

OBD scanner to the DLC allows I/M inspectors and vehicle repair technicians to read the
readiness status of the vehicle's various onboard monitors as well as any diagnostic trouble
codes (DTCs).

Readiness Code: A status flag stored by a vehicle's onboard computer which is different from
a DTC in that it does not indicate a vehicle fault, but rather whether or not a given monitor
has been run (i.e., whether or not the component or system in question has been checked to
determine if it is functioning properly).

Scanner or Scan  Tool: A PC-based or handheld device used to interface with a vehicle's
onboard computer for the purpose of reading DTCs and monitor readiness status.

Test-and-Repair: An I/M program which allows the same people who test a vehicle to also
repair the same vehicle and retest it to determine whether or not the repairs performed were
adequate.  Test-and-repair programs are also generally decentralized, though not all
decentralized programs are necessarily test-and-repair.

Test-Only: An I/M program - usually, though not exclusively centralized - which requires
that the functions of testing and repair be performed by different, financially unrelated

                   Data Link Connector Mapping Diagram

    Diagnostic Link Connector Mapping Diagram
     Driver Side
' /
             Passenger Side

            / ' i
       1  X
   -  Preferred Connector Location
               Vehicle Centerline

     Diagnostic Link Connector (DLC) Mapping Diagram Explanation

The mapping diagram of DLC locations contains a divided instrument panel (IP) with
numbered areas.  Each numbered area represents specific sections of the IP where
manufacturers may have located DLCs. This document briefly clarifies the numbered
locations on the mapping diagram.  Areas 1-3 fall within the preferred DLC location while
the remaining areas, 4-8, fall into the allowable DLC location according to EPA
requirements. Areas 4-8 require that manufacturers label the vehicle in the preferred location
to notify parties of the alternate  connector location.
Preferred Location(s)

Location #1:
This location represents a DLC positioned on the underside of the IP directly under the
steering column (or approximately 150mm left or right of the steering column). Visualizing
the underside of an IP divided into three equal parts from inside the passenger compartment,
this represents the center section.

Location #2
This location represents a DLC positioned on the underside of the IP between the steering
column and the driver's side passenger door. Visualizing the underside of an IP divided into
three equal parts from inside the passenger compartment, this represents the left section.

Location #3
This location represents a DLC positioned on the underside of the IP between the steering
column and the center console. Visualizing the underside of an IP divided into three equal
parts from inside the passenger compartment, this represents the right section.
Allowable Location(s)

Location #4
This location represents a DLC positioned on the upper part of the IP between the steering
column and the center console (but not on the center console, see location #6).

Location #5
This location represents a DLC positioned on the upper part of the IP between the steering
column and the driver side, passenger door.

Location #6
This location represents a DLC positioned on the vertical section of the center console and
left of the vehicle center line.
Location #7

This location represents a DLC positioned 300 mm right of the vehicle centerline either on
the vertical section of the center console or on the passenger side of the vehicle.

Location #8
This location represents a DLC positioned on the horizontal section of the center console
either left or right of the vehicle center line.  This does not include the horizontal section of
the center console that extends into the rear passenger area (see location #9).

Location #9
This location, not shown, represents any DLC positioned in an area other than those
mentioned above (e.g., in the rear passenger  area on the driver side armrest).

Vehicles with Hard-to-Find Data Link Connector Locations*, by Make and Model Year
                (*Location numbers refer to DLC map in Appendix B)

Manufacturer Year
Rolls- Royce
1996, 1997
1996, 1997
L 1997-2000
1996- 1998
1 996
Cabriolet, A6
3 Series
3 Series (including '96-'99 M3)
5 Series
X3/M Roadsier
F Series
Acura CL
Acura CL
Acura RL
Acura TL
Acura TL
NSX, 32,000
Acura RL
All Vehicles
Range Rover
New Hybrid
Previa (2/4 WD)
all vehicles except S80
Cabrio, Golf, Jetta
Location/ Comments
1 /cover
rear ashtray
in glove box

1/4 turn slot head screw
1/4 turn slot head screw
1/4 turn slot head screw
under stero cntri

passenger side of console
under passgr. dash

up high under the dash board

behind ashtray
under passgr. dash
bove shifter

in front of shifter behind ashtray
Behind ashtray

below radio next to seat heater control
under passgr. dash
under passgr. dash
under passgr. dash
under passgr. dash

console under passgr. dash
under passgr. dash
above shifter

passenger side center console front
n coin box

behind fuse box panel
above parking brake

Above Passenger Oash
behind fuse box panel
behind fuse box

driver's side of console
n glove box
under parcel tray
under passngr dash

behind plastic hinged cover
right side of steering column
behind fuse box panel
behind coin box

top instrumt panel
behind fuse box panel

in front of shifter under coin tray
hand brake area

right side of ashtray

on dash behind wiper lever

on dash behind wiper lever



                Manufacturers Known to Have OBD Readiness Issues

1996 Chrysler vehicles - Vehicles may clear readiness at key-off. Vehicles should be tested
normally.  If vehicles are found to be "Not Ready," they should be referred to a qualified
service provider so the OBD software can be updated.

1996 - 1998 Mitsubishi vehicles - These vehicles may have a high degree of "Not Ready" for
catalyst monitor due to a "trip based" design. Mitsubishi has provided driving cycles in its
service information to allow monitors to operate. These vehicles should be scanned for MIL
illumination without regard to readiness status.

1996 Nissan vehicles and 1997 Nissan 2.0 liter 200SX - These vehicles may have a high
degree of "Not Ready"for catalyst and evaporative monitors due to a "trip based" design.
Nissan has provided driving cycles in its service information to allow monitors to operate.
These vehicles should be treated as other non-problematic vehicles. Nissan Technical
Service Bulletin #NTB98-018, February 18, 1998.

1996-98 Saab vehicles - These vehicles may have a high degree of "Not Ready"for catalyst
and evaporative monitors due to a "trip based" design.  Saab has provided driving cycles in
its service information to allow monitors to operate. These vehicles should be treated as
other non-problematic vehicles.  Saab Technical Service Bulletin not yet available.

1996 Subaru vehicles - Vehicles will clear readiness at key-off. There is no reprogramming
available for this line of vehicles. These vehicles should be scanned for MIL illumination
without regard to readiness status. Subaru Technical Service Bulletin #11-49-97R (see
Appendix  F of this guidance).

1997 Toyota Tercel and Paseo - Vehicles will never clear the evaporative monitor to
"Ready."  At this time no fix is available. Vehicles should be scanned using remaining
readiness monitors as described for non-problematic vehicles.

1996 Volvo 850 Turbo - Vehicles will clear readiness at key-off.  There is no reprogramming
available for this line of vehicles. These vehicles should be scanned for MIL illumination
without regard to readiness status. Volvo Technical Service Bulletin #SB  2-23-0056.

1996-98 Volvo vehicles (excluding 850 Turbo) - These vehicles may have a high degree of
"Not Ready"for catalyst and evaporative monitors due to a "trip based" design. Volvo has
provided driving cycles in its service information to allow monitors to operate. These
vehicles should be treated as other non-problematic vehicles.  Volvo Technical Service
Bulletin #SB 2-23-0056.

                     OBD-I/M Test Procedure Flow Chart

                      Start OBD
                       I/M Test
/Vehicle fails
    test     /<-
 Turn ignition
 switch to the
"Off" position
for at least 12
                                           Locate DLC,
                                           connect test
                                          Note MIL (MIL
                                        illumination maybe
                                        brief) while turning
                                        ignition switch to
                                        the "Run" position
                                        with engine "Off1
  Does MIL
                                         Start and leave
                                       (engine running and
                                          with on-board
   Center for Automotive Science and Technology
          Weber State University

   approved test
                                        be established with the
test equipment
                                                                    Did the
                                                                 MIL illuminate
                                                            when ignition switch was
                                                              at "Run" position with
                                                                  the engine
                                                                    "Off" ?
 Vehicle fails
   (Note #2)
                                               Is MIL
                                           commanded on?
                                             (Mode $01,
 Vehicle fails
     test     K
  (Note #4)
                         Is the
                    MIL illuminated?
                  (Second chance to
                      pass "Bulb
                                                                  Vehicle fails  /
                                                                     test      /
Center for Automotive Science and Technology
       Weber State University

                    View Readiness Code
                    (Data collection only)
Retrieve DTCs using
 Mode $03 request.
 Provide DTC's with
  description on a
 Vehicle Inspection
Report for repair and
    fleet failure
    fails OBD
     I/M test
    Are minimum
 required Readiness
Codes set to "Ready"?
      (Note #6)
:                                         Vehicle is not ready
                                          for I/M evaluation.
                                         Vehicle needs to be
                                          operated in such a
                                         vay as to exercise all
                                              (Note #5)
      OBD I/M
    Center for Automotive Science and Technology
           Weber State University

Notes on flow chart:

Note 1:  The purpose of this step is to verify the On-Board Diagnostic (OBD) system has control of
         the Malfunction Indicator Light (MIL) and the MIL is functional. Operation of the MIL varies
         between vehicle manufacturers.  Key On Engine Off (KOEO) typically results in the MIL on
         steady, however, there are systems which will illuminate the MIL only briefly during KOEO.
         In either situation MIL presence and illumination capability has been established.
         If the vehicle fails the I/M test at this point, the vehicle inspection report should indicate the
         MIL problem should be repaired and also include information gathered during the
         remaining I/M test steps.

Note 2:  It is important for the I/M testing personnel to verify proper diagnostic equipment operation
         before failing the vehicle.  If the diagnostic equipment is functional then the vehicle's
         communication problem must be resolved.
         Without communication between the OBD system and the test equipment the I/M test must
         be ended and the problem resolved before further interrogation of the vehicle can be
         performed. This step includes identification  of Data Link Connector (DLC) tampering,
         serial data circuit problems and any other condition that would prevent the OBD system
         from communicating with the test equipment.

Note 3:  I/M test failure is a result of MIL illumination  even though the OBD system has not
         commanded the MIL on, or has stored any Diagnostic Trouble Codes (DTCs); e.g., a serial
         data line failure between the OBD computer and the Instrument Panel.

Note 4:  I/M test failure is a result of both the actual and commanded state of the MIL. DTCs should
         be stored since the MIL is commanded on.  A vehicle should not fail an I/M test when
         DTCs are stored but there is no MIL on; e.g., the DTC was stored by a loose gas cap which
         was subsequently tightened.

Note 5:  Readiness Code status must be identified at this stage  in the I/M test to determine whether
         or not all emission control systems have been tested by the OBD system.  If any one (or
         more) Readiness Code(s) are not set ("ready") the OBD system has not yet completed
         testing of the system(s) and failures may be  present but not yet identified.  It is important to
         understand that the vehicle does not fail the I/M test at this point; no emission related
         faults have been identified. The current state of the vehicle's emission control system is
         The emission control systems and related components  are tested under specific vehicle
         operating conditions. Therefore, to set the Readiness Codes the vehicle must be operated
         within these specific conditions (commonly referred to as "enable criteria") for the OBD
         system tests to be performed.  Once testing  of an emission control system is complete, the
         related Readiness Code will be set ("ready"). When all  Readiness Codes are set, the
         vehicle is ready for further I/M testing.
         It will be at the states discretion whether to recommend the customer drive the vehicle to
         set the Readiness Codes or to take the vehicle for service. The state may also choose to
         use a dynamometer drive cycle.

Note 6:  EPA has revised the current readiness code requirement to allow states to complete the
         testing process on model year 1996 thru 2000 vehicles with two or fewer unset readiness
         codes; for model year 2001 and newer vehicles, the testing process could still be complete
         provided there is no more than one unset readiness code. It is important to understand
         that the vehicle does not fail the I/M test because an unset readiness code is not itself an
         indication of an emission problem with the vehicle.