Permanent Diagnostic Trouble Codes

Beginning July 2019, the Bureau of Automotive Repair (BAR) will include Permanent Diagnostic Trouble Codes (PDTCs) as part of the Smog Check failure criteria for model-year 2010 and newer vehicles. This change will implement another On-Board Diagnostic (OBD) inspection improvement in accordance with California Code of Regulations, title 16, section 3340.42.2(c)(5). BAR has been conducting outreach on the use of PDTCs with the industry and vehicle manufacturers over the last year, including a BAR Advisory Group presentation and a separate workshop to gather input.

PDTCs use the same codes (i.e., P###) as regular Diagnostic Trouble Codes (DTCs), but cannot be erased without repairing the vehicle. PDTCs can only be cleared by the vehicle’s OBD system after it determines the problem that caused the PDTC is no longer present. PDTCs are set when a malfunction indicator light is illuminated and then stored on the vehicle’s computer.

In preparation of the rollout next year, BAR has been working with the Air Resources Board (ARB) and vehicle manufacturers to correct some manufacturer PDTC issues. In addition, vehicles with a PDTC will be allowed to pass a Smog Check inspection if the vehicle has been operated at least 15 warm-up cycles and has been driven at least 200 miles without the vehicle’s computer being reset. Early analysis indicates that the incorporation of PDTCs into the Smog Check Program could increase failure rates by 0.2 to 0.3 percent.

Currently, vehicles with readiness monitors not set for diesel after-treatment systems and gasoline evaporative control systems will pass a Smog Check inspection because these monitors can take an unusual amount of time to become set. The most frequently reported PDTCs seen in Smog Check data are for the diesel after-treatment and gasoline evaporative systems. PDTC detection with some minimum requirements on miles driven and warm-up cycles will be necessary criteria to ensure these systems are working correctly.

The lack of a PDTC could indicate that the vehicle is operating correctly even if some readiness monitors remain incomplete. For example, if a vehicle is rarely driven in a manner that completes a certain monitor, in some cases it could be ignored when the vehicle has no PDTCs stored. The use of PDTCs has the potential to reduce reliance on readiness monitors, assuring vehicle owners that their vehicles’ emission control systems are working correctly.

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