For 1990-2009 cars

### Diagnostic Instructions

• | Perform 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
--- | --- | --- | --- | ---
K2 Relay B+ | 2 | 2 | -- | --
Rear Defrost Switch Signal | B3743 5A | 2 | 2 | --
Rear Defog Relay Control | B0283 00 | B0283 00 | B0283 00 | --
Rear Defog Indicator Control | B0969 02 | 3 | B0969 01 | --
Rear Window Defogger Grid Control | 2 | 2 | 1 | --
Rear Window Defogger Grid Ground | -- | 2 | 2 | --
1. Rear Defogger Always On 2. Rear Defogger Inoperative 3. Rear Defogger Indicator Inoperative

### Circuit/System Description

When the rear defogger button is pressed a signal is sent to the rear fuse block which then supplies a ground to the K2 relay coil. The instrument panel cluster illuminates the rear window defogger indicator. B+ voltage is supplied at all times to the K2 relay. 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 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, refer to Rear Window Defogger Switch Malfunction.

2. Command the REC Heated Rear Window Test ON and OFF with a scan tool. The rear window defogger should turn ON and OFF when changing between the commanded states.

⇒ | If the rear window defogger does not turn ON and OFF when changing between the commanded states, refer to Rear Window Defogger Malfunction.

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

⇒ | If the rear window defogger indicator does not illuminate or continuously illuminates, refer to Rear Window Defogger Indicator Malfunction.

### Circuit/System Testing

#### Rear Window Defogger Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Ignition ON, verify the scan tool Defrost Switch parameter is Inactive.

⇒ | If not the specified value, test the signal circuit terminal 12 for a short to voltage. If the circuit tests normal, replace the IPC.

3. Connect a 5A fused jumper wire between the signal circuit terminal 12 and B+. Verify the scan tool Defrost Switch parameter is Active.

⇒ | If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.

4. If all circuits test normal, replace the HVAC control module.

#### Rear Window Defogger Malfunction

1. Ignition OFF, disconnect the K2 relay.
2. Ignition ON, verify a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

3. Verify a test lamp illuminates between the B+ circuit terminal 86 and ground.

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

4. Verify 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.

5. Disconnect the X2 harness connector at the rear window defogger grid.
6. Ignition OFF, test for less than 1 ohm between the ground circuit terminal 1 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. Ignition ON, connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the rear window defogger grid is activated.

⇒ | If the rear window 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 rear window defogger grid.

9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
10. Command the REC Heated Rear Window Test 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, replace the rear fuse block.

⇒ | If the test lamp is always OFF, replace the rear fuse block.

11. If all circuits test normal, test or replace the K2 relay.

#### Rear Window Defogger Indicator Malfunction

1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Ignition ON, command the Rear Window Defog LED Test OFF with a scan tool
3. Test for less than 1 volt between the control circuit terminal 13 and ground.

⇒ | If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the IPC.

4. Command the Rear Window Defog LED Test ON with a scan tool.
5. Test for greater than 9 volts between the control circuit terminal 13 and ground.

⇒ | If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.

6. If all circuits test normal, replace the HVAC control module.

### 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. 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.

#### Relay Test

1. Ignition OFF, disconnect the K2 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 25-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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Liftgate Window Replacement

Relay Replacement

Heater and Air Conditioning Control Replacement

Control Module References for IPC and rear fuse block replacement, setup, and programming