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 instrument panel module (IPM). The IPM will monitor the ignition mode switch only with battery voltage above 7 volts to prevent invalid input readings during low voltages encountered during vehicle cranking. If the ignition mode switch input or the battery voltage input changes, a ratiometric calculation of ignition mode switch input value is performed. The IPM discerns the following states over the ignition mode switch signal circuits:

To determine the correct power mode the IPM uses:

The following power modes are transmitted on both low speed and high speed GMLAN serial data circuits:

The accessory power mode times out after 20 minutes and the power mode becomes Off-Awake.

The following outputs are controlled by IPM as part of the power moding task:

Fail-safe Operation

The remote control door lock receiver (RCDLR) is the backup power mode master (BPMM). The both IPM and RCDLR receive signals from the ignition mode switch, representing the mode switch data, through 2 different circuits. The RCDLR can determine and transmit all the system power modes per the lists above. Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place if the power mode message is not received from the IPM or RCDLR. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode. The ECM and TCM behave differently.

Serial Data Messages

If no power mode message can be received, the modules remain in the last power mode received and check for the ERF message. If the ERF serial data is true, indicating that the engine is running, the modules fail-safe to Run power mode. In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is false, indicating that the engine is not running, the modules fail-safe to Off-Awake power mode and shut down after a while if no other conditions require them to be awake.

Discrete Power Mode Signals

Those modules that have Run/Crank signal inputs also remain in the state dictated by the last valid power mode message from the IPM or the RCDLR. They then check the state of their Run/Crank Ignition 1 voltage input to determine the current valid state. If the discrete ignition input is active, the modules will fail-safe to the Run power mode. If the discrete ignition input is inactive, the modules will fail-safe to Off-Awake power mode and shut down after a while if no other conditions require them to be awake.

ECM and TCM Power Mode Backup Strategy

The ECM and TCM remain in the last known power mode state until it can determine its backup system power mode based on their discrete Accessory voltage and Run/Crank Ignition 1 voltage inputs.