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Rear Window Defogger Malfunction (RPO C60)




Rear Window Defogger Malfunction (RPO C60)

Diagnostic Instructions

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

Diagnostic Fault Information





Circuit/System Description

When the rear defogger button is pressed, voltage is supplied to the relay coil and the body control module (BCM) also illuminates the rear window defogger indicator. Battery positive 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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Rear Window Defogger Description and Operation (Rear Window Defogger Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Manual HVAC Rear Defog Sw. parameter while pressing the rear defogger switch. The parameter should change between Off and On.

• If the value does not change between the commanded states, refer to HVAC Control Module Malfunction

2. Command the Rear Defog Relay ON and OFF with the scan tool. The rear window defogger and defogger indicator 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 Defogger Malfunction.
• If the rear window defogger indicator does not turn ON and OFF, refer to Rear Window Defogger Indicator Malfunction.

Circuit/System Testing

HVAC Control Module Malfunction
1. Ignition OFF, disconnect the X1 harness connector at the HVAC control module.
2. Test for less than 1 ohm between the ground circuit terminal A12 and ground.

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

3. Ignition ON, verify the scan tool Manual HVAC Rear Defog Sw. parameter is Off.

• If not the specified value, test the signal circuit terminal A5 for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3-amp fused jumper wire between the signal circuit terminal A5 and ground. Verify the scan tool Manual HVAC Rear Defog Sw parameter is On.

• If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

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

Rear Defogger Malfunction
1. Ignition OFF, disconnect the R/WDO 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. Disconnect the X2 harness connector at the rear window defogger grid.
6. Test for less than 1 ohm 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 X2 harness connector at the rear window defogger grid.
8. Connect a 30A fused jumper wire between the relay B+ circuit terminal 87 and the control circuit terminal 30. 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 control circuit terminal 86 and the ground circuit terminal 85.
10. Command the Rear Defog Relay 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 BCM.
• 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 BCM.

11. If all circuits test normal, test or replace the R/WDO DEFOG relay.

Rear Defog Indicator Malfunction
1. Ignition OFF, disconnect the X1 harness connector at the HVAC control module.
2. Disconnect the R/WDO DEFOG relay.
3. Connect a test lamp between the control circuit terminal 86 and ground.
4. Ignition ON, command the Rear Defog Relay 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 BCM.
• 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 BCM.

5. If all circuits test normal, test or 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.

Defog Switch
1. Ignition OFF, disconnect the X1 harness connector at the HVAC control module.
2. Test for infinite resistance between the signal terminal A5 and the ground terminal A12 with the switch in the open position.

• If not the specified value, replace the HVAC control module.

3. Test for less than 2 ohms between the signal terminal A5 and the ground terminal A12 with the switch in the closed position.

• If greater than the specified range, replace the HVAC control module

Defog Indicator
1. Ignition OFF, disconnect the harness at the HVAC control module.
2. Install a 5-amp fused jumper wire between the control terminal B5 and 12 volts. Install a jumper wire between the ground terminal A12 and ground. Verify the defog indicator illuminates.

• If the defog indicator does not illuminate, replace the HVAC control module

Relay Test
1. Ignition OFF, disconnect the R/WDO 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 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 (Verification Tests) after completing the diagnostic procedure.

* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Rear Window Replacement (Rear Window Replacement)
* Control Module References (Programming and Relearning) for HVAC control module and BCM replacement, setup, and programming

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