Pinpoint Test I : The Defrost System Is Inoperative: Notes
WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
Refer to Heated Window , for schematic and connector information.
Normal Operation
With the engine running, the HVAC module activates the rear window defrost relay by grounding the relay coil through circuit CH122 (WH/OG). 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 GD150 (BK/WH).
- DTC B1C83:12 (Rear Defog Relay: Circuit Short To Battery) - Sets when a short to voltage is detected on the relay control circuit by the HVAC module.
- DTC B1C83:13 (Rear Defog Relay: Circuit Open) - Sets when an open is detected on the relay control circuit by the HVAC module.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Rear window defrost relay
- Wiring, terminals or connectors
- FCIM
- HVAC module
- Open or short in rear window defrost grid