Normal Operation

When the engine is running and the defrost switch (integral to the HVAC module or Front Controls Interface Module (FCIM), if equipped with navigation system) is pressed, the HVAC module activates the rear window defrost relay by grounding the relay coil through circuit CH122 (WH/OG). For vehicles equipped with navigation system, the FCIM  sends the defrost request message to the HVAC module over the Controller Area Network (CAN). When the defrost relay is activated, power is supplied from the relay to the rear window defrost grid through circuit CRD06 (BN/YE). Ground is supplied to the rear window defrost grid through circuit GD147 (BK/VT).

• DTC B1C83:14 (Rear Defog Relay: Circuit Short to Ground or Open) - When the HVAC module senses an open or short to ground on the rear window defrost relay control circuit, this DTC will set.

This pinpoint test is intended to diagnose the following: 

• Wiring, terminals or connectors
• Rear window defrost relay
• HVAC module