Diagnostic Aids

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

The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
If the class 2 serial data circuit was shorted to ground, U1300 or U1305 will be set as history DTCs. Refer to DTC U1300, U1301, or U1305 .
If the class 2 serial data circuit was shorted to B+ U1301 or U1305 will be set as history DTCs. Refer to DTC U1300, U1301, or U1305 .