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.
Fog lamp relay
The fog lamp switch is a direct input to the BCM. The BCM sends a PCI Bus message to the FCM informing it to turn on the fog lamp relay. The fog lamp relay is then powered through low side control of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions. Fog lamp functionality is not equipped on all vehicles. The FCM "learns" that the vehicle is equipped with fog lamps by reading the BCM PCI Bus message.
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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.