Permanent Diagnostic Trouble Codes

  1. What are Permanent Diagnostic Trouble Codes?

    Permanent Diagnostic Trouble Codes (PDTCs) are very similar to regular Diagnostic Trouble Codes (DTCs). However, unlike regular DTCs, they cannot be reset by disconnecting the vehicle’s battery or cleared using an On-Board Diagnostic (OBD) scan tool. The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC and its corresponding DTC to set, and then allow the vehicle sufficient drive time to re-run the monitor that identified the problem in the first place. When the monitor runs without identifying a problem, the PDTC will clear itself.

  2. What regulations are applicable to PDTCs?

    Including PDTCs in the Smog Check Program will implement another OBD inspection development in accordance with California Code of Regulations, title 16, section 3340.42.2(c)(5).

  3. What outreach has been done to obtain stakeholder input?

    The Bureau of Automotive Repair (BAR) has been conducting outreach on the use of PDTCs with the industry and vehicle manufacturers, including two BAR Advisory Group presentations, a separate workshop, two BAR newsletter articles, and ET Blasts.

  4. When will PDTCs be included as part of the Smog Check inspection failure criteria?

    Starting July 1, 2019, the presence of PDTCs will be considered in determining the vehicle’s Smog Check inspection result.

  5. Why are PDTCs being included in the Smog Check Program?

    Unplugging the vehicle’s battery or using a scan tool are techniques sometimes used to clear OBD information for a vehicle that has an illuminated malfunction indicator light in an attempt to hide the fact that the vehicle is malfunctioning. Some of these vehicles can pass a Smog Check inspection before the vehicle can re-identify the underlying problem that set the malfunction indicator light and DTC(s). This can have a dramatic impact on air quality and decrease the effectiveness of the Smog Check Program. Although the use of readiness monitors reduces the chances of passing a Smog Check inspection with an active DTC, PDTCs can further ensure emission control systems are working correctly.

  6. How are PDTCs going to be used as part of a Smog Check inspection?

    Upon implementation, vehicles that have a PDTC stored in the OBD system will fail the Smog Check inspection regardless of whether the malfunction indicator light is illuminated. If a PDTC is stored, it indicates that the OBD system has not yet successfully verified that a previously detected emissions-related malfunction is no longer active.

  7. Which model-year vehicles will include PDTCs as part of the Smog Check inspection?

    The new criteria will apply to model-year 2010 and newer vehicles that support PDTCs.

  8. What if the vehicle does not properly support PDTC functionality?

    BAR is working with the Air Resources Board (ARB) to ensure that known problematic vehicles are addressed by the vehicle manufacturers. In the meantime, BAR will control application of such vehicles through the Smog Check database, and list them in the Smog Check OBD Reference, which is available on BAR’s website. Vehicles that do not support PDTC storage will not be subject to this part of the Smog Check inspection.

  9. What is the estimated increase in Smog Check inspection failure rate for the inclusion of PDTCs?

    BAR analysis indicates the new requirement could initially increase Smog Check inspection failure rates by less than half a percent (0.2 to 0.3%).

  10. Are there circumstances under which a PDTC will not cause a vehicle to fail a Smog Check inspection?

    Yes. PDTCs will be ignored if the vehicle has completed at least 15 warm-up cycles and been driven at least 200 miles since its OBD information was last cleared.

  11. Why will PDTCs be ignored when the vehicle has completed 15 warm-up cycles and been driven 200 miles since the codes were cleared?

    The time to complete 15 warm-up cycles and drive 200 miles is reasonable for vehicles to complete the self-diagnostic tests. In fact, most vehicles will complete the self-diagnostic tests well before this maximum limit is reached. The 15/200 limit is being established to prevent undue inconvenience to motorists who are trying to comply with the Smog Check Program requirements but are having trouble getting specific monitors to run to completion and ready for testing.

  12. Is there financial help available to consumers whose vehicles fail Smog Check for a PDTC?

    The Consumer Assistance Program (CAP) offers both repair assistance and vehicle retirement options to eligible consumers. Income-eligible consumers may receive financial assistance with emissions-related repairs if their vehicle fails a biennial Smog Check inspection. Consumers who meet eligibility requirements may receive up to $1,500 to retire their vehicle. Information about the Consumer Assistance Program is available at

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