Serial Data Power Mode: Notes

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 BCM. The BCM will monitor the mode switch only with battery voltage above 7 volts to prevent invalid input readings during low voltages encountered during vehicle cranking. If the mode switch input or the battery voltage input changes, a ratiometric calculation of mode switch input value is performed. The BCM discerns four thresholds:

• Inactive
• Start active
• Off active
• Short detect

To determine the correct power mode the BCM uses:

• The mode switch data received from the ignition mode switch
• The status of the Engine Run Flag (ERF)

The following power mode states are transmitted on the class 2 network:

• Off
• RAP
• Accessory
• Run
• Crank

The following power mode states are transmitted on the GMLAN network:

• Off
• Accessory
• Run
• Crank

The power mode message is a periodic with event message type and is transmitted by the PMM or BPMM at every 2 seconds on class 2 link and at every 250 ms on GMLAN link.

The Accessory power mode times out after 20 minutes and will transition to Off/Awake or RAP power mode.