Permanent Diagnostic Trouble Codes (PDTCs) are a specific type of OBD2 code that, unlike regular Diagnostic Trouble Codes (DTCs), cannot be simply erased. You might be familiar with clearing DTCs using a scan tool or by disconnecting your car battery, but permanent codes are designed to stick around until the underlying issue is properly resolved. This article will delve into what permanent OBD2 codes are, why they exist, and how they impact vehicle inspections and emissions testing.
What Exactly are Permanent Diagnostic Trouble Codes?
Think of Permanent Diagnostic Trouble Codes (PDTCs) as a more persistent version of regular DTCs. When your vehicle’s On-Board Diagnostic (OBD2) system detects a problem, it sets a DTC, often illuminating the check engine light. While standard DTCs can be cleared relatively easily, PDTCs are different. They are essentially “shadow” codes that remain stored in the vehicle’s computer even after a regular DTC is cleared.
The key difference lies in their reset mechanism. You cannot clear a PDTC using a standard OBD2 scan tool or by disconnecting the battery. The only way to get rid of a permanent code is to address the root cause of the problem that triggered the code in the first place. Once the issue is fixed, the vehicle needs to be driven through specific drive cycles to allow the OBD2 system to re-evaluate the system. If the monitor runs and confirms the problem is no longer present, the PDTC will clear itself automatically.
Why Were Permanent Codes Introduced?
Permanent Diagnostic Trouble Codes were implemented to enhance the effectiveness of vehicle emissions testing programs, like Smog Check in California. In the past, some vehicle owners would attempt to bypass emissions tests by clearing DTCs just before the inspection. This could temporarily turn off the check engine light, even though the underlying problem still existed. The vehicle might then pass the inspection, only for the problem and the DTC to reappear shortly after.
This practice undermined the purpose of emissions testing, which is to ensure vehicles are running cleanly and not polluting excessively. By introducing PDTCs, regulatory bodies aimed to prevent this manipulation. Even if someone clears the regular DTCs, the permanent code remains as evidence that an emissions-related issue was recently detected and may still be present. This ensures a more accurate assessment of a vehicle’s emissions system during inspections.
How Do Permanent Codes Affect Smog Checks and Vehicle Inspections?
Starting July 1, 2019, California’s Smog Check program began incorporating PDTCs into their inspection criteria. For model-year 2010 and newer vehicles that support PDTCs, the presence of a permanent code will result in a Smog Check failure, regardless of whether the check engine light is currently on.
This means that if a PDTC is stored in your vehicle’s OBD2 system, it indicates to the inspector that the OBD system has not yet verified that a previously detected emissions malfunction is resolved. Even if your car seems to be running fine and the check engine light is off, the PDTC will still trigger a failure.
Are There Any Exceptions?
Yes, there are limited circumstances where a PDTC will not cause a vehicle to fail a Smog Check inspection. PDTCs are disregarded if the vehicle has completed at least 15 warm-up cycles and has been driven at least 200 miles since its OBD system information was last cleared.
This 15 warm-up cycle/200-mile allowance is designed to provide sufficient time for the vehicle’s self-diagnostic systems to run all necessary tests after a repair or code clearing. In most cases, vehicles will complete these self-tests well before reaching these limits. This exception is in place to avoid unfairly penalizing drivers who are genuinely trying to address emissions issues but are experiencing difficulty getting certain monitors to complete and show as “ready” for testing.
What if My Vehicle Doesn’t Support PDTCs?
The PDTC requirement applies to model-year 2010 and newer vehicles that are designed to support this functionality. If your vehicle does not properly support PDTCs, it will not be subject to this aspect of the Smog Check inspection. The Bureau of Automotive Repair (BAR) and the Air Resources Board (ARB) are working to identify and address any vehicles with known issues related to PDTC functionality. Information about such vehicles is typically available in resources like the Smog Check OBD Reference.
Will Permanent Codes Drastically Increase Smog Check Failures?
Initial analysis by the BAR suggested that the inclusion of PDTCs would likely lead to a relatively small increase in Smog Check failure rates, estimated to be less than half a percent (0.2% to 0.3%). This indicates that while PDTCs are a significant factor in ensuring emissions compliance, they are not expected to cause a widespread increase in failures.
Financial Assistance for Emissions-Related Repairs
If your vehicle fails a Smog Check due to a PDTC or any other emissions-related issue, and you require repairs, financial assistance may be available. Programs like the Consumer Assistance Program (CAP) in California offer repair assistance and vehicle retirement options to eligible consumers. Income-eligible individuals may receive financial help with emissions repairs if their vehicle fails a biennial Smog Check. Vehicle retirement options are also available for those who qualify.
Key Takeaways about Permanent OBD2 Codes:
- Persistent Nature: Permanent codes cannot be cleared with scan tools or battery disconnection.
- Emissions Focus: They are designed to prevent circumvention of emissions testing.
- Smog Check Impact: PDTCs can cause Smog Check failure in applicable vehicles.
- Resolution Requirement: Fix the underlying issue to clear a PDTC.
- Drive Cycle: Vehicle needs to be driven to allow self-clearing after repair.
Understanding permanent OBD2 codes is crucial for vehicle owners, especially in areas with stringent emissions testing programs. If you encounter a permanent code, it’s a clear signal that your vehicle has experienced an emissions-related problem that needs professional diagnosis and repair to ensure both environmental compliance and optimal vehicle performance.
