A scan tool, while invaluable for diagnosing car problems, doesn’t directly “clear” diagnostic trouble codes (DTCs) in the way many people think. This article clarifies how different types of DTCs work and how to properly address them.
Understanding the nuances of Diagnostic Trouble Codes (DTCs) is crucial for effective vehicle maintenance. There are three primary categories of DTCs: Permanent, Pending, and History codes. Each behaves differently and requires a specific approach for resolution.
Permanent DTCs: Addressing the Root Cause
Permanent DTCs, as defined by the Bureau of Automotive Repair (BAR), are not erased by simply disconnecting the battery or using a scan tool. These codes indicate a persistent issue that needs to be fixed at its source. A scan tool can identify the problem area, but it cannot eliminate the underlying mechanical or electrical fault.
The only way to clear a permanent DTC is to repair the problem that triggered the code. Once the repair is complete, the vehicle’s onboard diagnostic system will re-run the relevant monitor during specific drive cycles. If the problem is genuinely resolved, the permanent DTC will clear itself automatically. Attempting to use a scan tool to clear a permanent code will be unsuccessful. The vehicle’s system is designed to ensure the problem is truly fixed, not just masked.
Pending DTCs: Intermittent Issues
Pending DTCs represent intermittent faults or issues that haven’t fully materialized into a confirmed problem. These codes often arise when the Powertrain Control Module (PCM) detects a potential issue but hasn’t observed it consistently enough to trigger a full DTC and illuminate the check engine light.
Typically, if the fault doesn’t reoccur within a specific number of warm-up cycles (often around 40), the pending code will clear itself. Conversely, if the problem continues, the pending code will transition into a full DTC, activating the check engine light and requiring further diagnosis. A scan tool is useful for identifying these pending codes, providing an early warning of potential problems.
History DTCs: Records of Past Issues
History DTCs serve as a log of previously resolved problems. These codes indicate faults that were once active but have since been rectified. While a scan tool can sometimes clear history codes, others require specific driving conditions or a double clearing procedure.
The persistence of some history codes is due to the specific diagnostic tests required for certain systems. These tests often necessitate particular operating conditions that might not be met during regular driving. Consulting the vehicle’s service manual is essential for understanding the specific requirements to clear these types of history codes. The manual will outline the necessary driving conditions or procedures for code clearance.
Conclusion: Addressing DTCs Effectively
While a scan tool cannot directly clear all types of DTCs, it is an invaluable tool for diagnosing car problems and identifying the underlying cause of trouble codes. Addressing the root cause of the issue is the only way to effectively resolve DTCs, ensuring proper vehicle function and preventing future problems. Understanding the different categories of DTCs, and how they behave, empowers car owners to take proactive steps in maintaining their vehicles. Remember, using a scan tool in conjunction with a vehicle-specific repair manual will provide the most comprehensive approach to troubleshooting and resolving DTCs.
