Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is power mode master. On this vehicle power mode master is Body Control Module (BCM). Power mode master receives 3 signals/circuits from ignition switch. These are Unlock (IGN0), Run/Crank (IGN1) and Accessory (ACC) ignition switch signals/circuits. To determine correct power mode power mode master uses:

• state of these signals/circuits, either switch closed, battery voltage = 1 or switch open, open = zero.
• sequence of switch closures received by power mode master.
• status of engine run flag.

Since operation of vehicle systems depends on power mode, there is a fail-safe plan in place should power mode master fail to send a power mode message. Fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.