Pinpoint Test F: the Defrost System Will Not Shut Off Automatically

Glass, Frames and Mechanisms

Pinpoint Tests

Pinpoint Test F: The Defrost System Will Not Shut Off Automatically

Refer to Wiring Diagram Set 56, Heated Window for schematic and connector information. Diagrams By Number

Normal Operation

The rear window defrost system is controlled by the HVAC module. The engine must be running for the rear window defrost system to operate. When the rear window defrost button is pressed, the HVAC provides a ground for the rear window defrost relay coil through circuit 688 (GY/LB). The rear window defrost relay coil is energized, providing battery voltage to the antenna module on circuit 186 (BN/LB). The antenna module then supplies voltage and ground to the rear window defrost grid.

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Rear window defrost relay
- HVAC module



PINPOINT TEST F: THE DEFROST SYSTEM WILL NOT SHUT OFF AUTOMATICALLY

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F1 CHECK THE INPUT FOR A SHORT TO GROUND


- Ignition OFF.
- Disconnect: Rear Window Defrost Relay.
- Ignition ON.
- Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.




- Is the resistance greater than 10,000 ohms?

Yes
GO to F3.

No
GO to F2.

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F2 CHECK CIRCUIT 688 (GY/LB) FOR A SHORT TO GROUND


- Ignition OFF.
- Disconnect: HVAC Module C228b.
- Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.




- Is the resistance greater than 10,000 ohms?

Yes
INSTALL a new HVAC module. TEST the system for normal operation.

No
REPAIR the circuit. TEST the system for normal operation.

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F3 CHECK CIRCUIT 186 (BN/LB) FOR A SHORT TO VOLTAGE


- Measure the voltage between rear window defrost relay pin 87, circuit 186 (BN/LB), harness side and ground.




- Is any voltage present?

Yes
REPAIR the circuit. TEST the system for normal operation.

No
INSTALL a new rear window defrost relay. TEST the system for normal operation.

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