An OBD2 scanner is a valuable tool for diagnosing car problems, but can it clear all codes? The answer isn’t a simple yes or no. Understanding the different types of diagnostic trouble codes (DTCs) is key to knowing what an OBD2 scanner can and can’t do.
Types of Diagnostic Trouble Codes (DTCs) and Clearing Them
There are three main types of DTCs: permanent, pending, and history codes. Each type behaves differently and requires a specific approach for clearing.
Permanent DTCs
Permanent DTCs, as the name suggests, are more persistent than regular codes. They can’t be cleared by simply disconnecting the car battery or using an OBD2 scanner. These codes indicate a serious issue that has been confirmed by the vehicle’s onboard diagnostic system. According to the Bureau of Automotive Repair (BAR), the only way to clear a permanent DTC is to fix the underlying problem that triggered the code. After the repair, the vehicle needs sufficient drive time for the system to re-run its diagnostic checks. If the problem is resolved, the permanent DTC will clear itself automatically.
Pending DTCs
Pending codes represent intermittent faults or issues that haven’t been fully confirmed by the vehicle’s Powertrain Control Module (PCM). These faults might be temporary glitches or require specific driving conditions to occur consistently. Typically, if the fault doesn’t reappear within a specific number of warm-up cycles (often around 40), the pending code will clear itself. However, if the problem persists and the PCM detects the fault in consecutive cycles, the pending code will mature into a full DTC, potentially illuminating the check engine light. An OBD2 scanner can sometimes clear pending codes, but this doesn’t resolve the underlying issue.
History DTCs
History codes are records of past problems that have been resolved. They serve as a log of previous diagnostic issues. Some history codes can be cleared with an OBD2 scanner, while others require specific driving conditions or a double code clearing procedure. The ability to clear history codes depends on the specific code and the vehicle’s make and model. Consulting the vehicle’s service manual is often necessary to determine the correct clearing procedure for history DTCs. These codes are helpful for diagnosing intermittent issues that might not be present during a current diagnostic scan.
Conclusion: OBD2 Scanners and Code Clearing
While an OBD2 scanner can read and sometimes clear certain types of diagnostic trouble codes, it’s not a magic fix. It’s crucial to understand that clearing a code doesn’t necessarily solve the underlying problem. For permanent DTCs, repairing the issue is the only way to clear the code. Pending codes might clear themselves if the problem is intermittent, and history codes provide valuable information about past issues. Using an OBD2 scanner in conjunction with a thorough understanding of DTCs can help diagnose and address car problems effectively. Always consult your vehicle’s service manual for specific instructions on clearing codes.
