Navigating the complexities of your vehicle’s onboard diagnostic system can be challenging, especially when the check engine light illuminates. While most drivers are familiar with Diagnostic Trouble Codes (DTCs) that can be easily cleared, there’s a less understood category known as Obd2 Permanent Codes, or Permanent Diagnostic Trouble Codes (PDTCs). These codes represent a significant evolution in vehicle emission monitoring and have specific implications for vehicle owners, particularly concerning smog checks and vehicle maintenance.
What Exactly are OBD2 Permanent Codes?
Permanent Diagnostic Trouble Codes (PDTCs) are a specific type of DTC that, unlike regular DTCs, cannot be simply erased using a scan tool or by disconnecting your car battery. They are designed to remain stored in your vehicle’s On-Board Diagnostic (OBD) system until the underlying issue that triggered the code is properly resolved and verified through the vehicle’s self-diagnostic monitors.
Think of PDTCs as persistent reminders. When your vehicle detects a fault in its emission control system, it sets both a regular DTC and a PDTC. While the regular DTC might be cleared, the PDTC stays put, acting as a historical record that a problem occurred and was potentially masked. The only way a PDTC will clear is when the vehicle itself confirms, through repeated self-testing over multiple drive cycles, that the problem is no longer present. This involves the vehicle’s monitors running and completing their diagnostic checks without detecting the fault again.
The Regulations Behind Permanent Codes
The introduction of PDTCs is not arbitrary; it’s rooted in regulations aimed at enhancing the effectiveness of vehicle emissions testing programs, such as Smog Check programs in regions like California. These regulations, like those outlined in the California Code of Regulations, title 16, section 3340.42.2(c)(5), mandate the inclusion of PDTCs in smog check inspections.
This regulatory push is a direct response to attempts to circumvent emissions testing. Historically, some individuals would clear DTCs just before a smog check, hoping to pass the test before the fault and the malfunction indicator light (MIL), commonly known as the check engine light, reappeared. PDTCs effectively close this loophole, ensuring a more accurate representation of a vehicle’s emission system health during inspections.
Why are Permanent Codes Important for Smog Checks?
The primary reason PDTCs are now a critical part of smog check inspections is to prevent vehicles with emission problems from passing inspection simply because their fault codes were recently cleared. Before PDTCs, clearing codes before a test could temporarily hide underlying issues, allowing malfunctioning vehicles to pass, at least until the system re-detected the fault. This practice undermined the effectiveness of smog check programs and negatively impacted air quality.
An illustrative image of an Engine Control Module (ECM), a key component of the OBD-II system that stores permanent codes.
PDTCs address this by providing a reliable indicator of past emission-related faults. Even if the check engine light is not currently on because codes were recently cleared, the presence of a PDTC signals to the smog check inspector that an emission issue occurred and has not been genuinely resolved and verified by the vehicle’s own diagnostic system.
Starting July 1, 2019, in California, the presence of PDTCs became a Smog Check failure criterion. This means that if a vehicle undergoing a smog check has any PDTCs stored in its OBD system, it will automatically fail the inspection, regardless of whether the check engine light is illuminated at the time of inspection.
Which Vehicles are Affected by PDTC Inspections?
The inclusion of PDTCs in smog check criteria generally applies to newer vehicles. Specifically, model-year 2010 and newer vehicles that are equipped to support PDTC functionality are subject to this aspect of the smog inspection. It’s important to note that not all vehicles, especially older models, necessarily support PDTCs.
For vehicles that do not properly support PDTC functionality, or have known issues with their PDTC systems, the Bureau of Automotive Repair (BAR) in California is working with the Air Resources Board (ARB) and vehicle manufacturers to address these issues. In the meantime, BAR manages the application of PDTC checks through the Smog Check database and provides a reference list of such vehicles in the Smog Check OBD Reference available on their website. Vehicles listed here or those that genuinely do not support PDTC storage will not be penalized for PDTCs during a smog check.
Will PDTCs Significantly Increase Smog Check Failures?
Initial analysis from BAR suggests that the inclusion of PDTCs has a relatively minor impact on overall Smog Check failure rates. Estimates indicate a potential initial increase of less than half a percent (0.2% to 0.3%). This suggests that while PDTCs are a crucial addition to emissions testing, they are primarily targeting vehicles with genuine, unresolved emission issues rather than causing widespread failures for vehicles that are properly maintained.
Are There Exceptions? When PDTCs Are Ignored
Yes, there are specific circumstances under which PDTCs will not cause a vehicle to fail a Smog Check inspection. To prevent undue inconvenience, especially when dealing with intermittent issues or monitors that take time to run, PDTCs are ignored if the vehicle has completed at least 15 warm-up cycles and has been driven at least 200 miles since its OBD information was last cleared.
This 15 warm-up cycle/200-mile exception is designed to provide ample driving time for vehicles to complete their self-diagnostic tests and for monitors to run and confirm that a previously detected fault is indeed resolved. In most cases, vehicles will complete these self-tests well before reaching these limits. This exception is in place to accommodate situations where drivers are genuinely trying to address issues and comply with smog check requirements but are experiencing delays in monitor completion.
Financial Help for PDTC-Related Smog Check Failures
For vehicle owners who fail a Smog Check due to PDTCs and require emission-related repairs, the Consumer Assistance Program (CAP) in California offers financial assistance. CAP provides both repair assistance and vehicle retirement options for eligible consumers. Income-eligible individuals may receive financial aid to help with emissions repairs if their vehicle fails a biennial Smog Check. Furthermore, the program offers options for vehicle retirement, providing financial incentives for retiring older, higher-polluting vehicles. More information about the Consumer Assistance Program is available on the BAR website.
Conclusion: PDTCs and Responsible Vehicle Ownership
OBD2 permanent codes are a vital advancement in vehicle emission control and smog check programs. They are designed to ensure that vehicles on the road meet emission standards and that temporary clearing of codes does not mask underlying problems. For vehicle owners, understanding PDTCs means recognizing the importance of addressing check engine lights promptly and thoroughly. If your vehicle has a PDTC, it’s a clear indication that an emission-related issue needs attention. Addressing these issues not only ensures your vehicle will pass smog checks but also contributes to cleaner air and better vehicle performance in the long run. If you are facing issues with permanent codes, it is advisable to consult with a certified mechanic to diagnose and properly repair the underlying problem.
