Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMN). On this vehicle the PMM is the Body Control Module (BCM). The BCM receives 2 signals/circuits from the ignition switch. These are the Ignition 1 and Ignition 3 signals/circuits.

To determine the correct power mode the BCM uses:

• The state of these signals/circuits, either switch closed (B+ = 1)or switch open (open = O)
• The status of the engine run flag.

The chart indicates the modes detected and transmitted by the BCM. See Fig 1.

Fig 1: Identifying BCM Modes

Courtesy of GENERAL MOTORS CORP.