Understanding and dealing with OBD2 codes is a crucial part of modern vehicle maintenance and repair. Among these codes, Permanent Diagnostic Trouble Codes (PDTCs) can be particularly perplexing. Unlike regular DTCs, permanent codes cannot be simply erased with a scan tool or by disconnecting the battery. This article provides an in-depth guide on how to address permanent OBD2 codes, ensuring your vehicle is running efficiently and can pass emissions inspections.
Understanding Permanent OBD2 Codes (PDTCs)
Permanent Diagnostic Trouble Codes, or PDTCs, are a specific type of diagnostic trouble code mandated in all OBD-II compliant vehicles since model year 2010 and in some earlier models. They are designed to ensure that vehicle emission problems are properly addressed and not just masked by simply clearing codes.
What Makes PDTCs Different?
The key difference between PDTCs and regular DTCs lies in their persistence. When a fault is detected in your vehicle’s emission control system, a regular DTC is stored. You can typically clear these codes using an OBD2 scanner. However, PDTCs are stored under the same conditions as regular DTCs but with a crucial distinction: they cannot be cleared by normal means.
This persistence is by design. Regulatory bodies like the EPA in the United States and similar organizations worldwide implemented PDTCs to prevent vehicles from passing emissions tests immediately after fault codes have been cleared, only for the problem to reoccur shortly after. PDTCs ensure that a vehicle truly undergoes repair and that the system verifies the fix before the code is removed.
Why Were Permanent Codes Introduced?
The introduction of PDTCs addresses a loophole in the older OBD-II systems. Previously, some vehicle owners or less scrupulous repair shops would simply clear the DTCs just before an emissions test. This could temporarily turn off the “Check Engine Light,” allowing the vehicle to pass the test, even though the underlying issue was still present. PDTCs close this loophole by requiring the vehicle itself to verify the repair over time through specific driving cycles before the code can be automatically cleared by the system.
Why Can’t You Just Delete Permanent Codes?
The inability to manually delete PDTCs is a core feature of the OBD-II system’s design. The system is set up to automatically clear these codes only when the vehicle itself determines that the fault is no longer active and the emission system is functioning correctly. This verification process involves:
- Fault Detection: The vehicle’s computer (ECU/PCM) detects an emissions-related fault.
- Code Setting: Both a regular DTC and a PDTC are stored in the system’s memory.
- MIL Illumination: The Malfunction Indicator Lamp (MIL), commonly known as the “Check Engine Light,” is illuminated to alert the driver.
- Verification Process: The vehicle then needs to go through a series of drive cycles where the diagnostic system re-runs the test for the fault condition. A drive cycle is not just a simple trip; it involves specific driving conditions like speed, engine temperature, and duration.
- Code Clearing (Automatic): If, during these drive cycles, the system determines that the fault is no longer present and the emission system is operating as expected, the PDTC will be automatically cleared by the vehicle’s computer. The MIL will also turn off.
Understanding the check engine light is the first step in addressing OBD2 issues.
Attempting to clear PDTCs with a scan tool will be unsuccessful. The “clear codes” function on a scanner will only erase regular DTCs, not the permanent ones. Disconnecting the vehicle’s battery will also not clear PDTCs; they are stored in non-volatile memory specifically designed to retain them even without power.
Steps to Address and Clear Permanent OBD2 Codes
Since you cannot directly delete PDTCs, the correct approach is to address the underlying issue that triggered the code in the first place. Here’s a step-by-step guide:
1. Identify the Permanent Code
The first step is to accurately identify the PDTC. You will need an OBD2 scanner to do this. Connect the scanner to your vehicle’s diagnostic port (usually located under the dashboard on the driver’s side). Run a scan for trouble codes. The scanner will display any stored codes, differentiating between regular DTCs and PDTCs. PDTCs are often indicated with a “P” prefix and may be flagged as “permanent” or “pending permanent.”
2. Understand the Code and Diagnose the Problem
Once you have the PDTC, research what it means. OBD2 codes are standardized, so a code like “P0420” generally refers to Catalyst System Efficiency Below Threshold (Bank 1). Online resources, repair manuals, and databases like those found on websites dedicated to OBD codes (like obd-codes.com) can provide detailed descriptions of each code, potential causes, and common symptoms.
Based on the code description, you need to diagnose the root cause of the problem. For example, a P0420 code could be due to a failing catalytic converter, faulty oxygen sensors, exhaust leaks, or other engine issues affecting combustion. Proper diagnosis may involve:
- Visual Inspection: Check for obvious issues like damaged wiring, vacuum leaks, or broken components.
- Sensor Testing: Use a multimeter or scan tool to test the functionality of relevant sensors (e.g., oxygen sensors).
- System Checks: Perform tests on related systems, such as the exhaust system for leaks or the fuel system for proper operation.
Using an OBD2 scanner is essential for reading and understanding diagnostic trouble codes.
3. Repair the Underlying Issue
After diagnosis, perform the necessary repairs to fix the problem. This could involve replacing a faulty sensor, repairing a leak, replacing a catalytic converter, or addressing engine performance issues. Ensure you are using quality parts and following proper repair procedures.
4. Verify the Repair
Once the repair is completed, it’s crucial to verify that the issue is actually resolved. Simply replacing parts without proper diagnosis might not clear the PDTC if the root cause is something else.
5. Initiate a Drive Cycle
After repair, the PDTC will not disappear immediately. You need to perform one or more drive cycles to allow the vehicle’s OBD-II system to re-evaluate the emission system and confirm the repair. A drive cycle is a specific set of driving conditions that prompts the vehicle’s computer to run various self-tests, including the one related to the PDTC.
Drive cycle procedures vary depending on the vehicle manufacturer, make, and model. General steps often involve a combination of:
- Cold Start: Starting the vehicle after it has been sitting for several hours (engine completely cooled down).
- Idling: Letting the engine idle for a specific period.
- Highway Driving: Driving at a steady speed on the highway for a certain duration.
- City Driving: Driving in stop-and-go traffic or at lower speeds.
- Deceleration/Coasting: Allowing the vehicle to coast down from higher speeds without using the brakes.
You can find specific drive cycle instructions in your vehicle’s repair manual or by searching online for “[your vehicle make model year] OBD2 drive cycle.” Some manufacturers also provide this information in the owner’s manual.
Important Considerations for Drive Cycles:
- Safety: Perform drive cycles in a safe location, obeying all traffic laws. Some steps might require open roads or specific speed maintenance.
- Patience: Drive cycles can take time to complete and may need to be repeated multiple times.
- Readiness Monitors: Use your OBD2 scanner to check the status of readiness monitors. These monitors indicate whether the vehicle’s self-tests have been completed. You want to see the relevant monitors associated with your PDTC (and ideally all emission-related monitors) set to “ready” or “complete.”
6. Check for Code Clearance
After completing the drive cycle(s) and ensuring the readiness monitors are set, re-scan your vehicle for OBD2 codes. If the repair was successful and the drive cycle was properly executed, the PDTC should be automatically cleared by the vehicle’s system. The “Check Engine Light” should also turn off if it was illuminated.
If the PDTC is still present, it indicates that either the repair was not effective in addressing the root cause, or the drive cycle was not completed correctly, or there might be another underlying issue. In this case, you may need to re-diagnose the problem, double-check your repair work, or repeat the drive cycle.
Vehicles with Known PDTC Issues
In some cases, certain vehicle models are known to have issues with PDTCs not clearing even after proper repair, often due to software glitches or design anomalies. The original article provides a valuable “Section E: Permanent Diagnostic Trouble Code Vehicles of Interest” which lists vehicles known to have PDTC problems.
Here is an excerpt from that list, highlighting some examples:
| Make | Year | Model | Engine (L); Fuel Type | Issue | Cause and Possible Remedy | Instructions to Inspector |
|---|---|---|---|---|---|---|
| Audi | 2010 | Q7 | 3.0 (TDI/diesel) | Permanent Fault Codes P0087, P0088, and P053F will not clear if present. | No remedy is available. | Test normally. BAR-OIS ignores these codes. |
| Chrysler | 2011-2015 | 200 | 2.4, 3.6 | Permanent Fault Codes will not clear. | Reflash per Recall V51. | Reflash then retest. |
| Dodge | 2011-2015 | Challenger | 3.6, 5.7, 6.4 | Vehicle fails for Permanent Fault Code U0140. | Reflash per Recall V51. | Reflash then retest. |
| Ford | 2011-2014 | Mustang | 3.7 & 5.0 (gasoline) | Vehicle fails for Permanent Fault Code P0315. | Vehicle not self-clearing permanent fault code. | Refer to Ford Customer Satisfaction Program 17N01. |
| Freightliner | 2014-2015 | Sprinter 2500 Sprinter 3500 (diesel) | – | Vehicle fails for Permanent Fault Codes P202A, etc. | Vehicle not self-clearing permanent fault code. | Test normally. BAR-OIS will ignore these codes. |
| Jeep | 2014-2017 | Grand Cherokee (diesel) | – | Vehicle fails for Permanent Fault Code P1D30. | Vehicle not self-clearing permanent fault code. | Test normally. BAR-OIS will ignore this code. |
If you own one of these vehicles and are facing persistent PDTC issues even after repair, consult the “Instructions to Inspector” column in the original table. It often indicates whether there’s a known software update, recall, or if the code should be ignored during an official inspection (like a Smog Check in California).
For vehicles listed with reflash remedies: Visiting a dealership for a software update (PCM/ECU reflash) is often necessary to resolve the PDTC clearing issue.
For vehicles where codes are ignored during inspection: In some specific cases, especially for older vehicles or known design limitations, inspection systems might be programmed to ignore certain PDTCs to avoid false failures. However, this does not mean the underlying issue should be ignored; it’s still best practice to diagnose and repair any emission-related problems.
PDTCs and Emission Testing (Smog Check)
Permanent Diagnostic Trouble Codes have a direct impact on vehicle emission testing, particularly in regions with stringent smog check programs. In many areas, including California, a vehicle will automatically fail a smog check if a PDTC is present, regardless of whether the “Check Engine Light” is on or off at the time of inspection.
This is because the presence of a PDTC indicates that a fault has occurred and, even if temporarily resolved, the vehicle’s system has not yet fully verified the repair through drive cycles. The smog check system is designed to detect PDTCs and fail the vehicle to ensure compliance with emission standards.
Exception: There’s a grace period in some inspection programs. For example, in California, PDTC presence is 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. This allows for normal driving and system verification after repairs.
Conclusion: Addressing PDTCs for Long-Term Vehicle Health
While you cannot simply “delete” permanent OBD2 codes, understanding how they work and how to properly address them is crucial for vehicle owners and technicians. The process involves accurate diagnosis, effective repair, and allowing the vehicle’s OBD-II system to verify the fix through drive cycles.
Focusing on proper repair, rather than just code clearing, ensures your vehicle operates efficiently, reduces emissions, and avoids issues with emission inspections. By following the steps outlined in this guide and being aware of vehicle-specific PDTC issues, you can effectively manage permanent OBD2 codes and maintain your vehicle’s health and compliance. Always prioritize addressing the underlying problem to truly “clear” a permanent code, ensuring long-term vehicle health and environmental responsibility.
