Serial Data Power Mode

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue. However, it is still accessible from the selected car via links, so may be relevant.

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 receives three signals/circuits from the ignition switch. These are the Acc/Run/Crank (IGNO), Run/Crank (IGN1) and Crank ignition switch 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 = 0)
The sequence of switch closures received by the BCM
The status of the engine run flag

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

Fig 1: Body Control System Description and Operation

Courtesy of GENERAL MOTORS CORP.