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.
Section 21 (Body Control Modules): Description
The Body Control Module (BCM) controls many vehicle functions. These functions include A/C compressor, audible warnings (chime), battery rundown protection, instrument panel cluster indicators and gauges, interior and exterior lighting, theft deterrent, keyless entry, rear compartment release, shift lock control (A/T) and panic horn.
The BCM communicates with other systems over a serial data line to execute various vehicle functions. This serial data line is referred to as the Class 2 serial data communication bus. 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.
Other modules that communicate with BCM over this line are Electronic Brake Control Module (EBCM), Powertrain Control Module (PCM), Instrument Panel Cluster (IPC), radio (IRC) and Sensing and Diagnostic Module (SDM).
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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.