Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Description & Operation
The Body Function Controller (BCM), located below left side of instrument panel to left of steering column, performs the following functions: reminder/warning functions, exterior and interior lighting control, battery rundown protection, locking functions, Remote Function Actuator (RFA) functions, overvoltage protection, retained accessory power, instrument cluster indicator control, theft deterrent, vehicle configuration storage, calibrations, and various communication and diagnostic operations.
BCM communicates with components using class 2 serial data line. Class 2 serial data line is used by various systems to share data information with other systems in order to execute various vehicle functions. Communication between each system is accomplished by sending digitally coded messages, which consist of specific information the system module must follow. Each system module is assigned its own recognition code, so that it can respond to appropriate messages. The BCM can determine state of health of other systems.
Signals that activate the BCM are known as "wake-up" signals. Multiple wake-up signals are necessary to sense both the insertion and removal of ignition key. BCM can enter a sleep state when key is in the ignition. BCM is asleep when it is not controlling or monitoring the following wake-up functions: Courtesy light switch; door jamb switch; door lock switch lock and unlock; an RFA signal; inadvertent power transition; or ignition is turned to OFF/UNLOCK, RUN or ACC position. The BCM will enter a sleep state when all of the following conditions exist: No activity on serial data line, ignition is turned off, no outputs are commanded, no delay timers are actively counting and no wake-up inputs are present.
BCM has 3 main power feeds and one main ground. Power for BCM's logic and internal driver operation is supplied through circuit No. 2340 (Orange wire). Power for door lock system is supplied through circuit No. 1540 (Orange wire). Power for courtesy lights is suppled through circuit No. 240 (Orange wire).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.