Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is Power Mode Master (PMM). On this vehicle PMM is Body Control Module (BCM). BCM receives 3 signals/circuits from ignition switch: ACC/RUN/CRANK (ignition 0), RUN/CRANK (ignition 1) and ACC/RUN (accessory).

To determine correct power mode, BCM uses following information:

• State of these signals/circuits, either switch closed (battery voltage = 1) or switch open (open = 0).
• Sequence of switch closures received by BCM.
• Status of engine run flag.