How to Fix Rear Defogger

Rear window defoggers use horizontal grid lines of conductive material applied to the rear window and energized with electricity to produce heat. Some basic checks and repairs may restore full function to a defogger if it's not working.

Instructions

1

Locate a good ground for the 12- vvolt test light near the rear window. Clamp the ground lead to the door striker, or seatbelt attaching screw and activate the system. Insert the test light probe into the back side of the electrical connector that plugs into the defogger grid. The test light should shine brightly. Repeat this procedure at the other end of the grid to ensure circuit continuity.

2

Check fuses or relays if the test light or the defogger power indicator fails to illuminate. Check the defogger relay if the defogger switch power indicator comes on without supplying power to the grid. The system may incorporate a timer mechanism that cuts power after 10 minutes of system operation. Monitor the power indicator to ensure system is energized while testing.

3

Consult a wiring diagram or component locator for your specific make and model vehicle to identify and locate system timers and relays. Replace any defective fuses or components and confirm voltage at the grid connector with the test light. Check the circuit breaker if the system repeatedly shuts down prematurely.

4

Stand outside the vehicle while shining a flashlight through the grid lines and note any scratches or missing material in the grid. Grid damage will result in partial operation, allowing some of the grid to heat while other areas do not. Make repairs to the grid surface with special conductive paint contained in repair kits. Repair kits are available at auto parts stores to replace missing grid material.