Description & Operation: Notes

Body Control Module (BCM) controls a number of functional systems. BCM is connected to class 2 serial data line. Many control signals are implemented through class 2 messages. BCM, which is power mode master, is responsible for sending power mode messages on serial data line to other modules. BCM functions include these following:

• HVAC afterblow control.
• Battery guard.
• Chime request.
• Content Theft Deterrent (CTD).
• Controlled power.
• Door lock and unlock.
• Exterior lighting control.
• Fuel door release.
• Fuel level.
• Interior lighting control.
• Retained Accessory Power (RAP).
• Rear defogger.
• Serial data power mode messages.
• Storage Mode.
• SIR deployment unlock.
• Time of day for radio display.
• Trunk release.
• Vehicle personalization.

Power mode is information used by various control modules on vehicle to determine operation. Power mode reflects ignition switch position as well as any power modes that are customer convenience items. If a control module does not receive a power mode signal, either a serial data message or a hard wire input, control module does not operate.

Power mode signal may be as simple as a battery voltage input wired to a particular ignition switch contact. If this is also battery voltage supply to module/device, module/device will only operate with ignition contact closed to battery voltage. An example of this is starter relay when it is wired directly to CRANK/START contact of ignition switch. When CRANK/START contacts are closed, starter relay is energized and provides a current source to starter and starter solenoid. When ignition switch leaves CRANK/START position, switch contacts open and starter relay is de-energized. This removes current source from starter and solenoid and starter operation stops.