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.
Circuit/System Description
The accessory voltage circuit is a positive voltage signal to wake up the from the body control module (BCM) to the engine control module (ECM) and the transmission control module (TCM). The signal is activated in 2 ways; any time the ignition switch is in the ACC or RUN position, or anytime the body control module (BCM) determines that communication is needed from the powertrain. When the ignition switch is in the ACC or RUN position, the accessory voltage circuit input from the ignition switch to the BCM is internally connected to the accessory voltage circuit output, and voltage is supplied to the modules. The BCM also supplies voltage to the accessory voltage circuit when it determines that communication is necessary with the powertrain and the ignition is not in the ACC or RUN position such as during remote start.
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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.