Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis 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 transmission control module (TCM) 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 Diagnostic System Check - Engine Controls .

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:
- TCM power is interrupted
- The ignition switch is turned OFF
- The battery voltage level is very low
- A poor connection at the diagnostic link connector (DLC)