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.
Rear Window Defogger Operation
Battery positive voltage is supplied through the RR DEFOG/HTD MIRRORS fuse in the IP fuse block to the rear window defogger relay switched input. With the ignition in the ON position, ignition voltage is supplied through the DRL/HVAC/TEMP/HTDST fuse in the IP fuse block to the rear window defogger relay coil. When you depress the rear window defogger switch, the HVAC control module illuminates the rear window defogger indicator and grounds the control circuit of the rear window defogger relay. This energizes the rear window defogger relay and allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided by G401.
When you start the engine and press the rear window defogger switch for the first time, the defogger cycle lasts for 10 minutes. Further operation results in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition to the OFF position and then back to the ON position.
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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.