Normal Operation and Fault Conditions

The HVAC module deactivates the rear window defrost relay whenever the ignition is turned OFF, the rear window defrost switch is pressed (while the defrost system is active) or after a 15 minute timer has elapsed. REFER to Rear Window Defrost .

If the defrost system is active with the ignition in the OFF position, the fault could be an inoperative rear window defrost relay (contacts stuck closed) or a short to voltage in the rear window defrost grid voltage circuit.

If the defrost system is active only when the ignition is in the ON position, the fault could be a short to ground in the rear window defrost relay control circuit or a HVAC module concern (driver active all the time).