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.
Body Control Modules: Operation
The Powertrain Control Module (PCM) and Body Control Module (BCM) share hardware and software in order to control A/C compressor clutch. The BCM performs the following software functions: limits low speed compressor operation, prevents clutch slippage, monitors for overpressure or high coolant temperature, determines low ambient pressure and controls compressor clutch.
Battery rundown protection (or battery guard) feature provides protection from excessive battery drain caused by high current loads that are accidentally left on. When ignition is turned off, a time-out period is started. If odometer reads less than 15 miles, time-out period will last for 3 minutes. If odometer reads more than 15 miles, time-out period will last for 20 minutes. When time-out expires, inadvertent power output is turned off.
Each time ignition switch is turned from ACC to RUN position, BCM controls an instrument cluster bulb check for a calibrated amount of time. During this bulb check, instrument cluster will perform a WOW (gauge needle sweep from low to high to low positions) check.
When BCM activates an indicator in the instrument cluster, it may also produce a chime. The following chimes are provided: key-in-ignition, headlights on, unfastened seat belt, turn signal on, parking brake warning, door ajar warning and check gauges.
Use the Manual With the Right Hardware
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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.
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