GM Full-Size Trucks 1988-1998 Repair Information

Clearing Codes


Stored fault codes may be erased from memory at any time by removing power from the ECM for at least 30 seconds. It may be necessary to clear stored codes during diagnosis to check for any recurrence during a test drive, but the stored codes must be written down when retrieved. The codes may still be required for subsequent troubleshooting. Whenever a repair is complete, the stored codes must be erased and the vehicle test driven to confirm correct operation and repair.

The ignition switch must be OFF any time power is disconnected or restored to the ECM. Severe damage may result if this precaution is not observed.

Depending on the electrical distribution of the particular vehicle, power to the ECM may be disconnected by removing the ECM fuse in the fusebox, disconnecting the in-line fuse holder near the positive battery terminal or disconnecting the ECM power lead at the battery terminal. Disconnecting the negative battery cable to clear codes is not recommended as this will also clear other memory data in the vehicle such as radio presets.