Diagnostic Trouble Codes (DTCs): Don't Just Clear Codes

As collision repair technicians, our expertise is not typically scanning and diagnostics related. However, the influx of technology, electrical components, and sensors into vehicles will require technicians to acquire a basic knowledge of scanning and diagnostics. A lot of information is provided from a scan tool, but what do we do with this information?

Diagnostic trouble codes (DTCs) are normally the main goal of scanning, however, DTCs are often misunderstood. There is a misconception in the collision repair industry that when the physical repairs are completed, you hook up a scan tool, and clear all codes. This should not be the typical process. In order to properly repair the vehicle, the DTCs need to be recorded, investigated, and a decision made on how they should be handled.

When a DTC comes up on the scan, this means that there is an error or problem in the system. The DTC could be from the accident, from the repair process, or a previous issue altogether. Simply deleting these codes can leave the door open for problems further on. If the code was from a previous issue, it could hinder future diagnostics.

The code may be telling you that:

• a calibration is needed.
• a sensor needs to be reset.
• there was a loss of communication with a module.
• a component has failed.

These are all actions that cannot be ignored. An example would be if a DTC says a calibration is needed. If the DTC is just deleted, the system may not reset the DTC until a certain distance is travelled. This means the system may not be functioning correctly.

Another example would be if parts were removed from a vehicle during the repair process and the DTCs were for loss of communication with those parts. These DTCs were most likely set due to the vehicle being started and moved while the parts were disconnected. These codes should be cleared and verified they are corrected. This is a digital fingerprint of the repair process and may confuse future diagnostics if left in the system.

The final example would be if there is an internal engine DTC that set months before the accident, that code should not be deleted. This may be information that a service technician will need at a later time to diagnose a problem unrelated to the collision.

Make sure to research and repair any relevant DTCs that you find when repairing the vehicles. Follow the OEM repair procedures and information to ensure a complete, safe, and quality repair.

Additional I-CAR Collision Repair News you may find helpful:

• ADAS, Calibration, And Scanning Article Hotspot

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Article validated in 2025