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
--- | --- | --- | --- | ---
Relay Switch B+ | 2 | 2 | -- | --
Rear Defogger Relay Control | B0283 02 or B0283 06 | B0283 05 or B0283 06 | B0283 05 | --
Rear Window Defogger Grid Control | 2 | 2 | 1 | --
Relay Coil Ground | -- | B0283 05 or B0283 06 | 2 | --
Rear Window Defogger Grid Ground | -- | 2 | 2 | --
1. Rear Defogger Always ON 2. Rear defogger Inoperative

### Circuit/System Description

When the rear defogger button is pressed, voltage is supplied to the relay coil by the HVAC control module which also illuminates the rear window defogger indicator. B+ voltage is supplied at all times to the relay switched input and the relay coil is always grounded. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger.

### 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 Verification

1. Ignition ON, observe the scan tool Rear Defrost Switch parameter while pressing the rear window defogger switch. The parameter should change between Active and Inactive.

⇒ | If the value does not change between the commanded states, replace the HVAC control module.

2. Observe the operation of the rear window defogger indicator while pressing the rear window defogger switch. The indicator should turn ON or OFF each time the rear window defogger switch is pressed.

⇒ | If the indicator does not turn ON or OFF with each switch press, replace the HVAC control module.

3. Command the Rear Defog Request ON and OFF with a scan tool. The rear window defogger should turn ON and OFF when changing between the commanded states.

### Circuit/System Testing

1. Ignition OFF, disconnect the RR DEFOG relay.
2. Test for less than 1 ohm between the ground circuit terminal 85 and ground.

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

3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 30 and ground.

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

4. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Ignition OFF, disconnect the X2 harness connector at the defogger grid.
6. Test for less than 5 ohms between the 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 defogger grid.
8. Ignition ON, connect a 40A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. Verify the defogger grid is activated.

⇒ | If the defogger grid does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the defogger grid.

9. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
10. Command the Rear Defog Request ON and OFF with a scan tool. 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 voltage. If the circuit tests normal, replace the HVAC control module.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

11. If all circuits test normal, test or replace the RR DEFOG relay.

### Component Testing

#### Relay Test

1. Ignition OFF, disconnect the RR DEFOG relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

⇒ | If greater than the specified range, replace the relay.

#### 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. The test lamp should be off when testing at the ground side of the grid and get brighter as the test lamp moves closer to the voltage supply side of the grid. The test lamp should be dim when testing each grid line in the middle.

⇒ | 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.

• | Liftgate Window Replacement

• | Relay Replacement

• | Control Module References for HVAC control module replacement, programming, and setup