Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

IMPORTANT:

Do not clear the DTC unless directed by a diagnostic procedure. Clearing the DTCs will erase all Freeze Frame and Failure Records stored in PCM memory.
Poor engine performance can sometimes be diagnosed as a transmission driveability condition. In order to avoid mis-diagnosis of the automatic transmission, always perform the Diagnostic System Check - Engine Controls in Engine Controls - 4.3L or in Diagnostic System Check - Engine Controls Engine Controls - 4.8L, 5.3L and 6.0L.

Use a scan tool that is known to function correctly. If necessary, test the scan tool on another vehicle.
Ensure the scan tool contains the most current file available.
The scan tool will display a loss of communication error message under the following conditions:
- PCM power is interrupted.
- The ignition switch is turned OFF.
- The battery voltage level is very low.
- A poor connection at the data link connector (DLC).