Rear Window Defogger Malfunction
Rear Window Defogger Malfunction
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 window defogger switch is pressed, voltage is supplied to the rear window defogger relay coil energizing the relay. The switch side of the energized relay closes allowing voltage to flow through the relay to the rear window defogger grid.
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)
Circuit/System Verification
Command the rear window defogger ON and OFF by pressing and depressing the rear defogger switch. The rear window defogger grid and rear window defogger indicator should turn ON and OFF when changing between the commanded states.
If the rear window defogger grid does not turn ON and OFF when changing between the commanded states, refer to Rear Window Defogger Malfunction.
If the rear window defogger indicator is always ON or always OFF, refer to Rear Window Defog Indicator Malfunction.
Circuit/System Testing
Rear Window Defogger Malfunction
1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Test for less than 1 ohm between the ground circuit terminal 2 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition OFF, connect the harness connector at the HVAC control module
4. Disconnect the DEFOGGER relay.
5. 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.
6. Verify a test lamp illuminates between the ignition circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
7. 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.
8. Ignition OFF, disconnect the X2 harness connector at the rear window defogger grid.
9. 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.
10. Connect the harness connector at the rear window defogger grid.
11. Ignition ON, connect a 25A 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.
12. Connect a test lamp between the control circuit terminal 86 and the ignition circuit terminal 85.
13. Command the rear window defogger ON and OFF with by pressing and depressing the rear window defog switch. 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 HVAC control module.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
14. If all circuits test normal, test or replace the DEFOGGER relay
Rear Window Defog Indicator Malfunction
1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Verify that a test lamp does not illuminate between the control circuit terminal 10 and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage, if the circuit tests normal, replace the I/P fuse block.
3. Disconnect the DEFOGGER relay.
4. Ignition ON, connect a 25A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify that a test lamp illuminates between the control circuit terminal 10 and ground.
• If the test lamp is not illuminated, test the control circuit for a short to ground or an open/high resistance, replace the I/P fuse block.
5. If all circuits test normal, replace the HVAC control module.
Component Testing
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 DEFOGGER relay.
2. Test for 60-180 ohm 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 95
* 85 and 87
• If not the specified value, replace the relay.
4. Install a 15A fused jumper wire between the relay terminal 85 and B+. Install a jumper wire between the relay terminal 86 and ground. Test for less than 2 ohm 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 (Within an Electrical Center) (Service and Repair)
* Rear Window Replacement (Rear Window Replacement)
* Heater and Air Conditioning Control Replacement (Hatchback) (HVAC - Manual)
* Heater and Air Conditioning Control Replacement (HVAC - Automatic)