United States Air and Radiation EPA420-R-00-014
Environmental Protection August 2000
Agency
vxEPA Analyses of the OBDII
Data Collected From the
Wisconsin I/M Lanes
> Printed on Recycled Paper
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EPA420-R-00-014
August 2000
the I/M
Ted Trimble
Transportation and Regional Programs Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
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.
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1.0 Summary and Conclusions
Since August 1998, Wisconsin's inspection and maintenance (I/M) program contractor,
Envirotest Systems Corporation, has been sending EPA staff onboard diagnostic (OBD) scanning
and IM240 test results data collected on model year (MY) 1996 and newer vehicles coming
through the Wisconsin I/M test lanes. The data provided by Envirotest includes vehicle
identification, and EVI240, OBD-I/M, and gas cap test results (for a full list of the 40 data fields
included in the Wisconsin data, see the Appendix A at the end of this report). In analyzing the
Wisconsin data, EPA focused on: 1) the readiness status of the OBD monitors 2) the frequency
of MIL illumination and 3) the relative failure rate of OBD-equipped vehicles based upon OBD-
I/M, IM240, and gas cap evaporative system testing. The following observations were made:
Regarding readiness
• The majority of vehicles showing up at the I/M lane with monitors reading "not
ready" were from MY 1996; the "not ready" rate for MY 1996 vehicles was 5.8%.
• Vehicle "not readiness" dropped off with each successive model year - to 2.2%
for MY 1997 and 1.4% for MY1998.
• If an exemption were allowed for up to two monitors to read as "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%.
Regarding MIL illumination
• After the first 40,000 miles, MIL illumination seems to increase with mileage and
age.
• The greatest MIL illumination rate was seen among MY 1996 vehicles (2.5%)
followed by MY 1997 (0.7%) and MY 1998 (0.5%).
Regarding the relative failure rate of OBD-I/M and other I/M tests
The OBD-I/M and IM240 tests fail roughly the same overall number of MY 1996
and newer vehicles but very few vehicles fail both tests.
• The stand-alone gas cap evaporative system leak test fails several times more
vehicles than does the OBD-based evaporative system monitor.
2.0 Background
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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 confidential to each
manufacturer and involve such things as ambient temperature as well as driving times and
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 test in question has been run), "not ready"
(meaning the test has not yet been run), or "not applicable" (meaning the vehicle is not equipped
with the components in question).
Current Federal regulations for OBD-I/M testing require that I/M programs reject from
further testing any MY 1996 or newer OBD-equipped vehicle that is found to have one or more
unset readiness flags. The reason vehicles with unset readiness flags are rejected but not failed is
because an unset readiness flag is not necessarily an indication of an emission problem. Rather,
it is an indication that certain monitor(s) that are intended to determine whether or not there may
be an emission problem have not been run to evaluate the system. In the case of rejection, the
issue of whether or not the vehicle requires repairs is deferred until the readiness flag(s) have
been set and the monitor(s) run.
To determine the extent to which vehicles may be appearing for their OBD-I/M check
with unset readiness flags in the real world, EPA looked at OBD readiness data from
Wisconsin's I/M program for the last five months of 1998 and the last eight months of 1999.
Wisconsin is currently conducting OBD-I/M checks in conjunction with a biennial, centralized,
IM240-based enhanced I/M program which also includes a separate gas cap pressure test. The
OBD-I/M check is only conducted on MY 1996 and newer light-duty vehicles and light-duty
trucks, and the results of the test are purely advisory (i.e., vehicles are not being rejected or failed
on the basis of the OBD-I/M check at this time).
The program data EPA analyzed included EVI240, gas cap, and OBD MIL illumination
and readiness data for over 116,000 MY 1996 and newer vehicles (see the Appendix A at the end
of this report for a full list of the 40 data fields included in the Wisconsin raw data). The data
was analyzed to determine the size of the readiness problem, the number of model years affected,
and the approximate percentage of vehicles that would be rejected under a variety of possible
readiness criteria. EPA also looked at the frequency of MIL illumination across model years and
vehicle types, and compared the relative failure rates of OBD-I/M to that of lane-based EVI240s
and gas cap tests. Lastly, EPA compared mileage accumulation and vehicle age data to MIL and
readiness rates to determine the impact of vehicle age and mileage.
3.0 Description of the Vehicle Sample
In performing the analyses discussed in this report, EPA used a sample of 116,669 MY
3
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1996 and newer, OBD-equipped vehicles coming through the Wisconsin I/M program, submitted
to EPA between August 1998 through December 1999. Although Wisconsin began OBD-I/M
checks in 1998, odometer data on the vehicles tested was not submitted to EPA until May 1999.
As a result, EPA does not have odometer data for MY 1997 vehicles (which received their first
OBD-I/M checks when they turned one year old in calendar year 1998). For the sake of its
analysis, EPA assumed that the mileage accumulation on MY 1997 vehicles after their first year
of operation was comparable to that of MY 1998 vehicles after their first year. Unlike the MY
1997 vehicles, EPA does have odometer data for the MY 1998 vehicles, which was gathered
when those vehicles received their first OBD-I/M check in 1999 (when they turned one year old).
Table 1 below presents the number of vehicles per model year included in the data set
EPA analyzed, including the period during which this vehicle data was gathered, and whether or
not odometer data was recorded. Omitting the first four months of 1999 because of the lack of
odometer data simplified these analyses. EPA does not believe that including the January - April
1999 data would have changed the conclusions drawn from this already very large sample.
Table 1: Model Year Profile of the Wisconsin OBD-I/M Data Set
MYs
1997
1996
1998
# of vehicles
22,602
50,297
43,691
Gathered during...
7/98 - 12/98
5/99 - 12/99
5/99 - 12/99
Odometer recorded?
No
Yes
Yes
The odometer data for these analyses was separated into mileage "bins" broken into 5,000
mile increments. Odometer readings were recorded in 1,000-mile units, using only the digits
before the comma with no attempt at rounding. Using this methodology, odometer readings of
9,000 and 9,999 miles would be considered equal, and both would be recorded as a 9. The
process of "binning" tends to introduce a certain amount of scatter to the data because vehicles
are not evenly distributed throughout the bin. Some bins will have a larger fraction of vehicles in
the top half of the bin and some in the lower half. To smooth the curves and make them easier to
read, EPA used a running average of three points as a filtering mechanism. Using this approach,
the values for bins 4,9,14 were averaged together and plotted as bin 9.
For the charts presented in this report, each data point represents a minimum of 150
vehicles. Table 2 below presents the maximum and minimum mileage for each vehicle
configuration, along with the actual number of vehicle records used for the limiting mileage.
Mileages below the minimum or above the maximum mileages listed in Table 2 were recorded
on fewer than 150 vehicles and were therefore excluded from the analysis performed to produce
the mileage accumulation based charts in this report. Table 3 shows the average mileage
accumulation in the sample, by model year.
Table 2: Minimum and Maximum Mileages
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Vehicles
1996LDV
1996LDT
1996 Total
1998LDV
1998LDT
1998 Total
min. mileage
9,000
14,000
9,000
4,000
4,000
4,000
# vehicles
342
172
413
1,076
429
1,505
max, mileage
99,000
94,000
109,000
59,000
59,000
69,000
# vehicles
197
182
174
207
191
185
Vehicle class
LDVs
LDTs
1996
45,385
51,018
1998
20,745
22,962
Chart 1 shows the number of vehicles in each mileage bin. Note that the 1998 vehicles
have considerably less mileage than the 1996 vehicles, as would be expected. There is no
odometer data for MY 1997 vehicles tested in calendar year 1998 but we expect that it will be
similar to the plotted MY 1998 data since both models were one year old when tested (as
previously discussed). Conversely, MY 1996 vehicles were three years old at the time of testing.
In a separate report1 an argument was made that trucks (LDTs) and cars (LDVs) should
be considered separately because they have different emission standards. In this report we also
keep LDTs and LDVs separate, creating six categories: 1996, 1997 and 1998 LDTs and LDVs.
The criteria used for separating cars from trucks were the IM240 cutpoints used in the I/M lane.
As a result, all vehicles subject to a hydrocarbon (HC) cutpoint of 0.6 gram per mile (gpm) were
considered LDVs. Using this approach leads to a slight distortion in the data because some small
trucks (i.e., the smallest 4 cylinder trucks like the S10 and Ranger) were classified as LDVs as
opposed to LDTs. EPA does not believe that this anomaly will have much impact on the general
conclusions drawn in this report.
4.0 Results
The results of EPA's analysis of Wisconsin's OBD-I/M data are presented below,
separated based upon the analysis focus areas discussed earlier: Readiness status, MIL frequency,
and test type comparison.
4.1 Readiness Status
"Evaluation of On Board Diagnostics For Use In Detecting High Emitting Vehicles" by Ed Gardetto and Ted
Trimble.
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4.1.1 Tabular Results
Table 4 below presents the "not ready" status for MY 1996-98 LDVs and LDTs in the
Wisconsin data set while Table 5 shows "not ready" status for the same model years, by monitor.
Note that the majority of the "not ready" vehicles are MY 1996 LDVs (6.9%) and that the
majority (77%) of all "not ready" MY 1996 LDVs were not ready for the catalyst monitor, while
MY 1998 LDVs were more frequently "not ready" for the evaporative system monitor. Note
further that by MY 1998, the "not ready" rate for LDVs dropped over five-fold - from 6.9% to
1.3% - while the overall "not ready" rate for MY 1996 vehicles (5.8%) dropped more than four-
fold by MY 1998 - to 1.4 %.
Table 4: "Not Ready" (MO Status for MY 1996-98
96LDV
%
96 LOT
%
96 Total
%
97LDV
%
97 LOT
%
97 Total
%
98LDV
%
98 LOT
%
98 Total
%
TOTAL
%
Total Tested
27,313
16,423
43,736
14,946
7,656
22,602
27,615
22,716
50,331
116,669
Not Readv (NR)
1,873
6.9%
651
4.0%
2,524
5.8%
360
2.4%
171
2.2%
531
2.3%
361
1.3%
350
1.5%
711
1.4%
3,766
3.2%
OneNR
1,155
4.2%
169
1.0%
1,324
3.0%
58
0.4%
34
0.4%
92
0.4%
101
0.4%
69
0.3%
170
0.3%
1,586
1.4%
TwoNR
884
3.2%
64
0.4%
948
2.2%
30
0.2%
14
0.2%
44
0.2%
61
0.2%
32
0.1%
93
0.2%
1,085
0.9%
Table 5: "Not Readv" Status for MY 1996-98 (By Monitor)
96LDV
%
Total Tested
27,313
Catalyst
1,435
5.3%
Evap
475
1.7%
O2
826
3.0%
Heated O2
880
3.2%
EGR valve
1,041
3.8%
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96 LOT
%
96 Total
%
97LDV
%
97 LOT
%
97 Total
%
98LDV
%
98 LOT
%
98 Total
%
TOTAL
%
16,423
43,736
14,946
7,656
22,602
27,615
22,716
50,331
116,669
471
2.9%
1,906
4.4%
87
0.6%
88
1.1%
175
0.8%
105
0.4%
221
1.0%
326
0.6%
2,407
2.1%
184
1.1%
659
1.5%
209
1.4%
77
1.0%
286
1.3%
287
1.0%
182
0.8%
469
0.9%
1,414
1.2%
74
0.5%
900
2.1%
38
0.3%
11
0.1%
49
0.2%
59
0.2%
32
0.1%
91
0.2%
1,040
0.9%
186
1.1%
1,064
2.4%
102
0.7%
31
0.4%
133
0.6%
61
0.2%
55
0.2%
116
0.2%
1,313
1.1%
72
0.4%
1,113
2.5%
33
0.2%
18
0.2%
51
0.2%
55
0.2%
17
0.1%
72
0.1%
1,236
1.1%
As discussed above, the Wisconsin data includes test results from MY 1997 and MY
1998 vehicles that were receiving their first tests on their one-year anniversary of purchase.
Unfortunately, as we also discussed above, EPA does not have mileage accumulation data for
MY 1997. Nevertheless, in the absence of any compelling reason to assume that MY 1997
vehicles were driven more or less than their MY 1998 counterparts in their first year of operation,
we believe it is reasonable to assume that MY 1997 and MY 1998 vehicles exhibited
comparable, accumulated mileage. The fact that the data in Table 4 still shows a significant
decline in "not ready" rate from MY 1997 to MY 1998 - from an overall average of 2.3% to
1.4% - suggests that manufacturer learning curve is at least a likely explanation for the
significant trend toward improvement in observed "not ready" rates. Chart 5 provides a graphic
illustration of this trend in readiness by model year.
In performing its analysis of the Wisconsin data, EPA also looked at the impact of
adjusting "not ready" rates based upon a variety of possible readiness waiver scenarios. In Table
4 above, the column headed "One NR" reflects the "not ready" rate by model year and vehicle
type adjusted to reflect a waiver of the "not ready" rejection requirement if only one monitor is
listed as "not ready." The column headed "Two NR" reflects a similar adjustment of the "not
ready" rate, but this time assuming a waiver of the rejection requirement if up to two monitors
are listed as "not ready." Table 4 shows that if any one monitor is allowed to be "not ready" the
overall rejection rate among MY 1996-98 vehicles goes from 3.2% to 1.4%. If exemptions are
allowed for vehicles with up to two unset readiness flags, the overall rejection rate goes down
even further - to 0.9%. Table 4 also breaks out the readiness status of the vehicles in the
Wisconsin data by monitor.
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4.1.2 Graphic Results
Chart 6 shows the effect of each monitor on the total readiness of the MY 1996 vehicles,
while Charts 7 and 8 show the same for MY 1997 and MY 1998 respectively. Note that the
catalyst monitor was the most important factor in determining MY 1996 vehicle readiness but in
MY 1997 and MY 1998, the evaporative system monitor also played a significant role.
Chart 9 shows the relative readiness of MY 1996 vehicles plotted against mileage
accumulation. Note that the trendline is similar to the MIL illumination trendline for MY 1996
vehicles presented in Chart 3 (i.e., a third order polynomial). A break at about 40,000 miles is
evident in both charts, although not as dramatic as seen in Chart 3. Also there does not seem to
be the same break in the truck curve and trucks are relatively "more ready" than cars. Chart 12
shows the same information as Chart 9, but for MY 1998 LDVs and LDTs. Because fewer
vehicles are "not ready" among the MY 1998 vehicles, there is more scatter in the data, but the
break at 40,000 miles is still evident.
Chart 10 shows the readiness of all the individual monitors in the MY 1996 LDTs. The
vehicle trendline plotted is a straight line (i.e., a first order polynomial). The first and second
orders are almost indistinguishable. Also shown is the strong influence of the catalyst monitor
on the readiness of these vehicles. Chart 11 presents the same information as Chart 10, but for
MY 1996 LDVs instead of LDTs. Again the catalyst monitor has a strong influence and now the
break at 40,000 is quite evident.
Chart 13 shows the readiness of all the individual monitors on MY 1998 LDTs. As can
be seen, the readiness of MY 1998 trucks is basically a function of the readiness of the catalyst
and evaporative system monitors. Chart 14 shows the same information as does Chart 13, but for
MY 1998 LDVs. In the case of MY 1998 LDVs, vehicle readiness is almost exclusively a
function of the readiness status of the evaporative system monitor
4.2 MIL Frequency
4.2.1 Tabular Results
Currently, EPA has very little data concerning how the average motorist reacts to the
MIL (also known as a "Check Engine" light). For the sake of this analysis, however, EPA
assumed that the people of Wisconsin knew that their vehicles would not be failed for having the
MIL on and so had no problem going to the I/M lane with it illuminated.
Table 6 below shows the number of vehicles in the Wisconsin OBD data set that were
tested by model year and vehicle type, as well as the number and percent of such vehicles with
the MIL commanded on. As was the case with readiness status, the majority of MIL-on vehicles
were from the 1996 model year.
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Table 6: MIL-on Frequency in the Wisconsin Data Set
Vehicle
1996 LDV
1996 LOT
1996 Total
1997 LDV
1997 LOT
1997 Total
1998 LDV
1998 LOT
1998 Total
Number tested
27,310
16,420
43,730
14,946
7,656
22,602
27,630
22,720
50,350
Number w/ MIL on
645
436
1,081
91
66
157
118
123
241
Percent w/ MIL on
2.4%
2.7%
2.5%
0.6%
0.9%
0.7%
0.4%
0.5%
0.5%
4.2.2 Graphic Results
In Chart 2 we see that 2.5% of MY 1996 vehicles appeared in the I/M lanes with the MIL
illuminated but only 0.7% of MY 1997 vehicles and 0.5% of MY 1998 vehicles were so
afflicted. EPA assumes that mileage is not a factor in the difference between MY 1997 and MY
1998 but may be a factor in the difference between MY 1996 and either MY 1997 or MY 1998
vehicles. The reason for this assumption is the fact that MY 1996 vehicle test results represent
three-years-worth of accumulated mileage, while MY 1997 and MY 1998 both represent only a
single year of mileage accumulation each. EPA has no data concerning how many of these
vehicles may have had a MIL illumination in the past which resulted in a repair, regardless of
model year or warranty status.
Chart 3 shows the change in MIL illumination of MY 1996 vehicles with mileage. EPA
notes a decline in MIL illuminations until about 40,000 miles, followed by a noticeable increase
in MIL illuminations. Although a continuous trendline is best represented by a third order
polynomial, two straight lines could just as easily represent the data; the break is so evident. It
should be noted that the warranty period for comprehensive coverage on these vehicles expires at
36,000 miles. Chart 4 shows the same information as Chart 3, but for MY 1998 vehicles. There
is more scatter to the data this time because the MIL illumination levels were about half what
was observed for MY 1996. MY 1998 LDVs and LDTs are not very different with regard to MIL
illumination rates up to 40,000 miles, but LDVs were found to have noticeably fewer MIL
illuminations at mileages over 40,000 miles.
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4.3 Test Type Comparison
4.3.1 MIL-on and IM240 Failure Rates
Table 7 below compares the relative failure rates for OBD-I/M versus IM240 observed in
Wisconsin, and the degree to which the test results overlap. As can be seen from the data, OBD-
I/M almost always fails slightly more vehicles than does the IM240 (MY 1998 LDVs are the
only exception).
Table 7: OBD-I/M Fails vs. EVI240 Fails
MY/Class
1996 LDV
1996 LOT
1996 Total
1997 LDV
1997 LOT
1997 Total
1998 LDV
1998 LOT
1998 Total
Total
Tested
27,313
16,422
43,735
14,944
7,656
22,600
27,616
22,716
50,332
OBD Fail
(number)
645
436
1,081
91
66
157
118
123
241
OBD Fail
(percent)
2.4%
2.7%
2.5%
0.6%
0.9%
0.7%
0.4%
0.5%
0.5%
IM240 Fail
(number)
569
383
952
71
51
122
223
47
270
IM240 Fail
(percent)
2.1%
2.3%
2.2%
0.5%
0.7%
0.5%
0.8%
0.2%
0.5%
Failed
Both
(number)
59
100
159
7
0
7
7
0
7
Failed
Both
(percent)
0.2%
0.6%
0.4%
0.2%
0.0%
0.0%
0.0%
0.0%
0.0%
Table 7 also makes clear that the agreement between IM240 and the OBD-I/M check is
exceedingly low for all model years and vehicle types, with the level of agreement dropping for
the newer of the OBD-equipped model years. What is not clear from this data is which of the
two tests is more beneficial to the environment. Determining which of the two tests — OBD-I/M
versus IM240 — is more effective is outside the scope of this analysis, but was addressed as part
of a separate pilot study performed by EPA between September 1997 and October 1999,
involving 201 in-use MY 1996 and newer OBD-equipped vehicles which each received OBD-
I/M, EVI240, and federal certification tests2.
' "Evaluation of On Board Diagnostics For Use In Detecting High Emitting Vehicles" by Ed Gardetto and Ted
Trimble.
10
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4.3.2 Gas Cap Testing vs. OBD-I/M
Unlike the OBD exhaust test versus the IM240, where the failure criteria for OBD are
tighter than the failure criteria for the IM240, the OBD failure criteria for leak detection are
known to be more lenient than the gas cap pressure test currently in use in several states.
Although in theory this difference in test stringency should result in a greater number of failures
for the gas cap test than for the OBD-based evaporative system test, it is not obvious that
vehicles actually develop such "in between" leaks in the real world. To shed light on this issue,
EPA looked at the Wisconsin data, focusing on the relative failure rates for the OBD-based
evaporative system test versus the gas cap pressure test. The results of that comparison are
presented in Table 8 below.
Table 8: Gas Cap vs. OBD Evaporative System Failure Rates
MY/Class
1996 LDV
1996 LOT
1996 Total
1997 LDV
1997 LOT
1997 Total
1998 LDV
1998 LOT
1998 Total
Total Tested
27,313
16,422
43,735
14,944
7,656
22,600
27,616
22,716
50,332
Gas Cap Fail
(number)
291
245
536
83
48
131
170
155
325
Gas Cap Fail
(percent)
1.1%
1.5%
1.2%
0.6%
0.6%
0.6%
0.6%
0.7%
0.6%
OBD Evap Fail
(number)
7
3
10
2
1
3
6
1
7
OBD Evap Fail
(percent)
0.03%
0.02%
0.02%
0.01%
0.01%
0.01%
0.02%
0.004%
0.01%
Note that the gas cap failure rate is several orders of magnitude higher than the OBD-I/M
failure rate for the entire evaporative emission system. Clearly, some of this is due to the fact
that enhanced OBD evaporative system monitoring was phased in over the model years being
looked at in this sample3. Furthermore, as described in our earlier discussion on OBD readiness,
the overall OBD readiness on MY 1998 LDVs was dominated by vehicles which showed up at
the test lane without their evaporative system monitors having run.
5.0 Conclusions
' The phase-in requirements for MY 1996, 1997, 1998, and 1999+ are 20%, 40%, 90% and 100%, respectively.
11
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Based upon its analysis of the Wisconsin OBD data set, EPA concluded the following:
• MIL illuminations increase with mileage and age, although MY 1996 vehicles
show a definite decline until about 40,000 miles when a noticeable increase
occurs.
• 5.8% of MY 1996 vehicles that showed up in the I/M lanes were not ready.
Allowing the test to be performed with two monitors not ready cuts the rejection
rate to 2.2% for MY 1996 vehicles. The number of not ready vehicles is much less
among MY 1997 and MY 1998 vehicles, although that may be due to the fewer
miles driven.
• Conclusions regarding vehicle trends based on an average mileage of 22,000 (MY
1997 and MY 1998) are not as strong as the conclusions based on MY 1996 data,
with an average mileage accumulation of about 48,000 miles.
• OBD-I/M and IM240 fail about the same number of vehicles but very few
vehicles fail both tests.
• The gas cap leak check fails significantly more vehicles than does the OBD-I/M
evaporative system test.
6.0 Next Steps
EPA continues to receive data from the Wisconsin I/M program and intends to continue
to monitor this data through calendar year (CY) 2000. Based upon past experience, EPA
estimates that this will mean an additional 85,000 records for MY 1997 vehicles and an
additional 85,000 records for MY 1999 vehicles will be available for analysis by the end of the
calendar year. It will be interesting to see how this data compares with the current data set. For
example, it is possible the differences that we see now among the MY 1996-98 vehicles may
prove to be mileage and/or age related and not so much the result of vehicle improvements. In
the current data set discussed in this report, the MY 1997 vehicles are similar to the MY 1998
vehicles in terms of age (i.e., both are one year old, as previously discussed) and, presumably,
mileage accumulation, while the MY 1996 vehicles are unique in being three years old. By
contrast, the MY 1997 vehicle data collected during CY 2000 will be for vehicles that are now
three years old and these may show the same mileage patterns that were seen among MY 1996
vehicles in the data set discussed in this report. Similarly, the MY 1999 vehicle data gathered in
CY 2000 should compare to the current MY 1998 vehicle data. Lastly, there may also be an
opportunity to compare some individual MY 1997 vehicles to their results from the previous test
cycle 2 years earlier.
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Appendix A: Wisconsin I/M and OBD Data Fields
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
0
R
s
T
U
V
W
Date/time
Mod yr.
Make
Model
Vin
Test
HCStan
Co Stan
NOx
HC
Co
NOx
Em fsec
Em res
Prcap
Stan
Pr cap ini
Prcap
Pr cap res
Onboard
Obd res
Trno
Codel
Code2
Date and time the vehicle was tested
Model year
Make
Model
Vin number
Test number, 1 for the first time vehicle has been tested in this test
cycle, 2 for the first retest. A very few vehicles have been retested up
to four times.
Final cutpoints, 0.6 grams per mile for cars
Final cutpoints, 1.5 grams per mile for cars
Final cutpoints 0.7 grams per mile for cars, Wisconsin does not fail
for NOx
Actual emissions total grams divided by the total miles,
the test was terminated
Actual emissions total grams divided by the total miles,
the test was terminated
Actual emissions total grams divided by the total miles,
the test was terminated
at the time
at the time
at the time
Number of seconds that the test ran. ( "0" for the full 240 second test)
P or F, pass or fail the I/M240 tailpipe test
Pressure cap standard, inches of water
Initial pressure, inches of water
Final pressure, inches of water
P or F, pass or fail pressure cap test
Whether the technician could find the OBD connection.
where he could not after October 98
No cases
Pass or fail
Number of codes present (sum of V through AA) but is
wrong
sometimes
The next six columns list the OBD trouble codes, if any
13
-------
X
Y
Z
AA
AB
AC
AD
AA
AF
AG
AH
AI
AJ
AK
AL
AM
AN
CodeS
Code4
Code5
Code6
Ready
misfire
Fuel
Comp
Cat
Heat
Evap
Sair
Acsys
Oxy
Hoxy
Egr
ObdMil
Odo
The next 1 1 columns list the readiness flags. 0 means that the
monitor is not fitted. 1 means that the monitor is fitted but not ready.
2 means that the monitor is ready
Fuel trim
Various circuits necessary for the other monitors to work
Catalyst
Heated catalyst
Evaporative system
Secondary air
Air conditioning
Oxygen sensor
Heated oxygen sensor
Exhaust gas recirculation sensor
Mil light, 1 if lighted, 0 if not. Should be same as column T
Odometer reading to nearest 1,000 miles (truncated)
14
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Appendix B: Criteria of Failure
Wisconsin judges that a vehicle has failed OBDII if a DTC is revealed. Thus if a
code number appears in column V there is an "F" recorded in Column T. For the purposes
of this report a vehicle is considered to have failed the OBDII test if the number 1 appears
in column AM, which signifies that the MIL is commanded on. All three of these columns
are generated by the computer and no visual check of the light is made.
Wisconsin judges that a vehicle has failed a cutpoint if the recorded value is above
the cutpoint by any amount. In other words no rounding to the correct number of
significant figures occurs.
A number of vehicles that fail the cutpoints after a full 240 seconds are passed in
the Wisconsin system. This apparently occurs because of the notion that a vehicle passes if
it passes either of two tests, the fast pass or the full 240. A vehicle can fast pass for HC and
CO but not NOx. It would then go the full 240 seconds but because Wisconsin does not fail
for NOx, these vehicles would be considered to have passed the fast pass algorithms and
would receive a passing grade even if they failed the full 240 second test. This brings into
question the effectiveness of the algorithms for the tier 1 vehicles. For this report all
vehicles that were above the cutpoints for any of the three pollutants after a 240 second test
were considered failures of the 240 test.
15
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CHART 1
^VEHICLES IN EACH MILEAGE BIN
7000
6000
5000
0)
-S 4000
3000 -
2000
1000
~~YM^^
20
40
60 80
mileage bins
100
120
140
-------
CHART 2
MIL ILLUMINATIONS
3.00
0.00
96car 96 truck total
97 car 97 truck total
98 car 98 truck total
-------
CHART 3
1996 VEHICLES WITH MIL ON
10
9
7 --
O
^
<
I 5
^=-1IE-0£
£W
-R±
^&
-l).1077x
«9C2
-f/T
20
40
60
MILEAGE BINS
80
100
car
truck
total
Poly, (total)
120
-------
CHART 4
1998 VEHICLES WITH MIL
2.5
1.5
0.5 --
10
20
= n
Z
0.01S4X
30 40 50
MILEAGE BINS
60
70
•car
•truck
total
•Poly, (total)
80
-------
CHART 5
Readiness by model year
8.0
7.0
6.0
5.0 --
re
p
J: 4.0
o
3.0
2.0
1.0
0.0
cars
trucks
totals
-------
CHART 6 1996 veh not ready
8.0
7.0
6.0
5.0 --
re
p
J: 4.0
o
3.0
2.0
1.0
0.0
vehicles n.r.
cat
evap
oxy
Hoxy
egr
-------
CHART 7
1997 veh not ready
3.0
2.5 --
2.0
re
£ 1.5
o
c
1.0
0.5
0.0
vehicles n.r.
cat
evap
oxy
Hoxy
egr
-------
CHART 8
1998 veh not ready
2.0
1.8
1.6
1.4
1.2
re
p
J: 1.0
o
0.8
0.6
0.4
0.2
0.0
Dears
• trucks
Dtotals
vehicles n.r.
cat
evap
oxy
Hoxy
egr
-------
CHART 9 1996 VEHICLES NOT READY
0 +-
20
40
60
MILEAGE BINS
80
100
-cars
-trucks
totals
•Poly, (totals)
120
-------
CHART 10
1996 TRUCKS NOT READY
a
•cat
•evap
Oxy
Hoxy
•trucks n.r.
•Linear (trucks n.r.)
0 10 20
30 40 50 60
MILEAGE BINS
70 80 90 100
-------
CHART 11
1996 CARS NOT READY
a
LU
a:
O
z
^
0 +-
20
40
60
MILEAGE BINS
80
100
—*—cat
—•—evap
Oxy
—x—Hoxy
-*-Egr
cars nr
. (cars nr)
120
-------
CHART 12
1998 VEHICLES NOT READY
2.5
2.0
Q
1.5
1.0
0.5
0.0
\o,
TZJ
32
10
20
30 40
MILEAGE BINS
50
60
70
-cars
-trucks
totals
•Poly, (totals)
80
-------
CHART 13
1998 TRUCKS NOT READY
a
—•—cat
—•—evap
Oxy
—x— Hoxy
-*-Egr
—•—trucks n.r.
. (trucks n.r.)
-0.5
MILEAGE BINS
-------
CHART14
1998 CARS NOT READY
a
10
20
30 40
MILEAGE BINS
50
60
cat
evap
Oxy
Hoxy
gr
cars n.r.
Poly, (cars n.r.)
70
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