WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
The number below refers to the step number on the diagnostic table.
4. If the battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.