An OBD2 scanner is a crucial tool for diagnosing car problems, but sometimes it can’t clear codes. This can be frustrating, but understanding why this happens and knowing the different types of diagnostic trouble codes (DTCs) can help you troubleshoot the issue. Let’s explore the reasons why your OBD2 scanner might not be clearing codes and what steps you can take.
Different Types of Diagnostic Trouble Codes (DTCs)
There are several types of DTCs, each with unique characteristics that affect how they are cleared:
Permanent Diagnostic Trouble Codes (PDTCs)
Permanent DTCs are stubborn. Unlike regular codes, disconnecting the battery or using an OBD2 scanner won’t clear them. The Bureau of Automotive Repair (BAR) clarifies that a PDTC indicates a persistent problem that needs to be fixed. The code will only clear itself after the underlying issue is resolved and the vehicle’s monitoring system re-runs without detecting the fault. Essentially, clearing a PDTC requires fixing the root cause of the problem, not just erasing the code. Your OBD2 scanner, unfortunately, can’t bypass this process.
Pending Diagnostic Trouble Codes
Pending codes signal intermittent problems or issues that haven’t fully matured into a DTC. These codes appear when the Powertrain Control Module (PCM) detects a fault but hasn’t confirmed it in two consecutive warm-up cycles. If the problem doesn’t reappear within 40 warm-up cycles, the pending code will vanish automatically. However, if the issue persists, it graduates to a full DTC, triggering the check engine light. An OBD2 scanner can sometimes clear pending codes, but it won’t resolve the underlying problem if one exists.
History Diagnostic Trouble Codes
History codes are records of past issues that have been resolved. They serve as a log of previous malfunctions, helpful for diagnosing intermittent problems. Clearing history codes varies. Some can be erased with a scan tool, while others need a double clearing process or specific driving conditions to be met. Your car’s service manual will detail the specific requirements for clearing each history code. While an OBD2 scanner can be useful for clearing some history codes, it’s not always a guaranteed solution.
Conclusion: Fixing the Problem, Not Just the Code
When your OBD2 scanner won’t clear codes, remember that the code itself is just a symptom. The real solution lies in diagnosing and fixing the underlying mechanical issue. Understanding the different types of DTCs – permanent, pending, and history – is critical to effectively troubleshooting car problems. For persistent issues or those involving permanent DTCs, consult a qualified mechanic to diagnose and repair the problem properly. While an OBD2 scanner is a valuable tool, it’s not a magic wand. Fixing the car is the ultimate way to clear those stubborn codes.
