Power Mode Mismatch: Description
WARNING: This page is about a different car, the 2003 GMC Envoy XL and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
On vehicles that have several control modules connected by serial data circuits, one module is the Power Mode Master (PMM). On vehicles covered in this article, the PMM is the Body Control Module (BCM). The BCM uses 3 signals from the ignition switch. These are the Ignition 0, Ignition 1, and Accessory.
Normal vehicle class 2 communications and module operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by the BCM in order to determine the correct power mode. The BCM communicates the system power mode to all class 2 modules on the class 2 serial data line.