For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Rear Window Defogger Relay Switch B+ | 1 | 1 | -- | --
Rear Window Defogger Relay Coil Ignition | 1 | 1 | -- | --
Rear Window Defogger Relay Control | 2 | 1 | -- | --
Rear Window Defogger Control | 1 | 1 | 2 | --
Rear Window Defogger Grid Ground | -- | 1 | -- | --
1. Rear Window Defogger Inoperative 2. Rear Window Defogger Always On

### Circuit/System Description

The rear window defogger is controlled by the rear defogger relay through a high side drive control circuit. Battery voltage is supplied to the switch side of the relay at all times and when the relay is energized battery voltage is supplied to the rear window defogger control circuit. The rear defogger relay is controlled by the HVAC control module through a low side drive control circuit. Ignition voltage is supplied to the relay coil and when the rear defogger switch is pressed the relay control circuit is grounded and the relay will be energized.

### Reference Information

#### Schematic Reference

Defogger Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Rear Window Defogger Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information.

### Circuit/System Testing

1. Ignition OFF, disconnect the rear defogger relay.
2. Ignition ON, verify that a test lamp does not illuminate between the rear window defogger control circuit terminal 87 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignitionn circuit terminal 86 and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace rear defogger relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the rear window defogger control circuit terminal 87 for a short to ground.

5. Disconnect the X2 harness connector at the rear window defogger grid.
6. Test for less than 10 ohms between the defogger grid ground circuit terminal A and ground

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the rear window defogger grid.
8. Connect a 30 A fused jumper wire between the B+ circuit terminal 30 and the rear window defogger control circuit terminal 87. Verify the rear window defogger is activated.

⇒ | If the rear window defogger does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, repair or replace the rear window defogger grid.

9. Connect a test lamp between the ignition circuit terminal 86 and the relay control circuit terminal 85.
10. Cycle the rear window defogger switch ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the rear window defogger switch.

⇒ | If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the rear window defogger switch.

11. If all circuits test normal, test or replace the rear defogger relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Rear Window Defogger Braided Lead Wire