United States             Air and Radiation         EPA420-F-98-002
                   Environmental Protection                         January 1998

                   Office of Mobile Sources
&EPA       Regulatory
                  Proposed Amendment to On-Board
                  Diagnostic Checks Requirement for
                  I/M Programs
                   The U.S. Environmental Protection Agency (EPA) is proposing to
                   extend, by a period of three years, the deadline by which states must
                   implement On-Board Diagnostic (OBD) checks as a regular part of their
                   I/M programs. Prior to this proposed new deadline of January 1, 2001,
                   states may opt to include OBD checks and fail vehicles based on OBD
                   failure alone. States may not earn emission reduction credit, however,
                   unless exhaust and evaporative tests are performed as well. Should
                   EPA and states complete testing and review of OBD systems sooner
                   than expected, the Agency may be able to make credits available to
                   states who choose to implement OBD I/M checks prior to the proposed

                  On August 6, 1996, EPA published a final rulemaking relating to the
                  implementation of OBD checks as a routine part of I/M programs. In the
                  rule, EPA interpreted the Clean Air Act requirement to include both
                  emission testing and OBD checks and thus required both tests as part of
                  the regular I/M test procedures. Ozone Transport Region (OTR) areas
                  with OTR low enhanced programs were to implement OBD checks by
                  January 1, 1999, and all other areas were to implement OBD checks by
                  January 1, 1998. Until January 1, 2000, OBD checks, exhaust tests and
                  evaporative system tests, where applicable, were to be required on each
                  subject vehicle of model year 1996 and newer. After January 1, 2000,
                  failure of the OBD test would require mandatory repair.
                                                         I Printed on Recycled Paper

Overview of Proposed Rule
This rule proposes to delay the required implementation date for OBD by
setting the new implementation deadline as January 1, 2001, for all areas
with basic and enhanced I/M programs. This amounts to a two year delay
for OTR low enhanced areas and a three year delay for all others. During
this time extension, EPA will work with states and other stakeholders to
generate, collect and analyze the data necessary to determine the effec-
tiveness of OBD systems in an I/M setting.

EPA is currently conducting such a study which began October 1, 1997.
Two years are needed to ensure ample time for fleet penetration of OBD-
equipped vehicles, so that enough vehicles can be recruited for the study.
A third year will be needed to allow sufficient time to analyze the data
generated by the study.

In addition, EPA is proposing certain clarifying amendments to allow for
updates  to the Code of Federal Regulations which are cross-referenced in
the OBD rule. Section 86.094-17, which includes the technical specifica-
tions for OBD systems,  is periodically updated to include new require-
ments. This rule proposes to amend the sections of the OBD rule where
that subsection is referenced with new language which obviates the need
for future amendments in this regard.

This proposed rule does not affect the requirement that states revise their
I/M State Implementation Plans by August 6, 1998, to include the OBD
checks. Also unchanged are the sections which allow states the option to
implement OBD inspections before December 31, 1999, and to allow
failure of OBD to result in failure of the I/M test, thereby requiring
repair. However, states which choose to conduct OBD checks cannot earn
emission reduction credits for doing so unless they also perform the
exhaust  and evaporative tests, where applicable, or unless EPA completes
its analysis and  determines appropriate credit sooner than expected.
Effect of Proposed Rule
This proposed rule will allow the states even greater flexibility in design-
ing and implementing I/M programs which meet their local needs and
help them to move towards attainment. In addition, it will reduce the cost
burden the states would face if they were required to run OBD checks
concurrently with  the exhaust and evaporative tests as required by the
previous rule, so this amendment will produce a net savings. The I/M

testing requirements will now be less burdensome in terms of test time,
equipment and cost. Furthermore, it is not certain that the requirement
would have generated additional emission reductions to justify the added

OBD equipment suppliers and I/M contractors may need to adjust to
shifting requirements resulting from this proposed rule. Automobile
manufacturers will  see a delay in the generation of some data on OBD
in-use performance. The general public will not be affected by the
proposed delay, as it only postpones a requirement to which most have
not yet been subjected.

The proposed delay will have no appreciable effect upon the environ-
ment. The vehicles  which would otherwise be subject to the OBD check
will still receive exhaust and evaporative (where applicable) testing, if
the state is earning  emission reduction credits for those vehicles. Emis-
sion reductions will still be achieved for those vehicles despite the delay
in OBD checks.
For More Information
Additional documents on I/M programs and OBD are available elec-
tronically from the EPA Internet server at:


Document information is also available by contacting Russ Banush at:

  U.S. Environmental Protection Agency
  Office of Mobile Sources
  2565 Plymouth Road
  Ann Arbor, Michigan 48105
  (734) 668-4333