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, PMM is the Body Control Module (BCM). BCM receives 3 signals/circuits from ignition switch. These are ACC/RUN/CRANK (IGN 0), RUN/CRANK (IGN 1), and CRANK. BCM uses following to determine correct power mode:

• State of signals/circuits, either switch closed (B+ = 1) or switch open (open = 0).
• Sequence of switch closures received by BCM.
• Status of engine RUN flag.