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 Description
The ambient light sensor is a light sensitive transistor that sends a variable voltage signal to the body control module (BCM) in response to the exterior light level. The BCM energizes the DRL relay by grounding the DRL relay control circuit. The DRL operate when the ambient light sensor indicates daytime, the ignition switch is in the RUN position, the gear selector is not in the park position, and the parking brake is in released. The DRL can be manually turned OFF by depressing the AHL/DRL DEFEAT switch in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF the DRL and turns ON the DRL OFF lamp in the headlamp switch by grounding the DRL OFF indicator control circuit.
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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.