Symptom Related Diagnostic Procedures

Rear Window Defogger Inoperative

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information






Circuit/System Description

The HVAC control module controls the rear window defroster through the REAR DEFOG relay located in the underhood fuse block. When the rear defroster is activated the HVAC control module supplies battery voltage through the defroster relay control circuit to energize the relay coil.

Circuit/System Testing

1. Ignition ON, verify that the rear defogger indicator illuminates when the switch is activated.

• If the indicator does not illuminate when system operation is attempted, replace the HVAC control module.

2. Connect a test lamp from the supply side of the REAR DEFOG fuse to ground.
3. Verify that the test lamp is illuminated while the rear defogger is turned on.

• If the test lamp does not illuminate test the battery supply circuit to the REAR DEFOG relay for an open/high resistance or short to ground. If the circuit tests normal replace the REAR DEFOG relay.

4. Disconnect the rear defogger grid connectors and verify that a test lamp illuminates when connected from battery voltage to the ground circuit connector.

• If the test lamp does not illuminate repair the ground circuit for an open/high resistance.

5. Connect a test lamp across the rear defogger grid connectors and verify that the test lamp illuminates when the defogger is turned on.

• If the test lamp does not illuminate repair the defogger grid supply circuit for an open/high resistance.

6. If the circuits test normal replace the rear window defogger grid.

Component Testing

Rear Window Defogger Grid Test

1. Ignition ON, turn on the rear window defogger.
2. Verify that a test lamp illuminates between each rear window defogger grid line and ground.

• If the test lamp remains bright at the middle of the grid line, test for an open between the test point and the ground side of the grid.

• If the test lamp remains off at the middle of the grid line, test for an open between the test point and the voltage supply side of the grid.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Rear Window Replacement
* Control Module References for HVAC control module replacement, programming, and setup Programming and Relearning