Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the Body Control Module (BCM). The BCM uses 3 signals from the ignition switch. These are the Ignition 0 (Unlock), Ignition 1 (Run/Crank), and Accessory.

To determine the correct power mode the BCM uses:

• The state of these signals
• The sequence of switch closures received by the BCM
• The status of the engine run flag

The chart indicates the power modes detected and transmitted by the BCM:

Fig 1: Correct Ignition Switch Inputs

Courtesy of GENERAL MOTORS CORP.