When you turn the ignition switch to the ON position, voltage is supplied through the RR DEFOG fuse to the rear defogger relay switch. Battery positive voltage is supplied at all times to the rear defogger relay coil. When you press the rear defogger button, the instrument panel integration module (IPM) sends a Class 2 message to the rear integration module (RIM) to enable the rear defogger relay. The RIM energizes the rear defogger relay by grounding the control circuit of the rear defogger relay, allowing voltage to the rear defogger. The RIM then sends a Class 2 message to the IPM requesting illumination of the rear defogger LED.

When you turn the ignition switch to ON and press the rear defogger switch for the first time, the defogger cycle lasts 10 minutes. Further operation results in 5 minute defogger cycles. The defogger cycle resets to 10 minutes when you cycle the ignition switch to the OFF position and then back to the ON position. The defogger cycle will remain on with vehicle speed greater than 30 mph, unless the defogger is manually turned off.