Heated Glass Element: Testing and Inspection
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) provide an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Battery positive voltage is supplied through the REAR DEFOG fuse located in the right rear fuse block to the REAR DEFOG relay switch input. When the rear window defogger switch is depressed, the HVAC control module sends a message via GMLAN serial data to the rear integration module (RIM) to enable the rear window defogger. The RIM energizes the REAR DEFOG relay by grounding the rear defog relay control circuit. This allows battery voltage from the relay switch input through the switch contacts and out the relay switch output to the rear window defogger. The RIM then sends a message via GMLAN serial data to the HVAC control module requesting the illumination of the rear window defogger indicator. Ground for the rear window defogger grid is provided by G403 and G404.
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)
Circuit/System Verification
1. Ignition ON, observe the rear defogger switch indicator while turning the rear defogger switch ON and OFF. The indicator should turn ON and OFF as the switch is activated.
• If the rear defogger switch indicator does not illuminate, refer to Rear Window Defogger Switch Malfunction.
2. Ignition ON, with a scan tool observe the rear defog status parameter while turning the rear defogger switch ON and OFF. The reading should change between ON and OFF.
• If the reading does not change as the switch is activated, refer to Rear Window Defogger Switch Malfunction.
• If the reading changes as the switch is activated, refer to Rear Window Defogger Malfunction.
Circuit/System Testing
Rear Window Defogger Switch Malfunction
1. Ignition ON, with a scan tool observe the rear defog status parameter while turning the rear defogger switch ON and OFF. The reading should change between ON and OFF.
• If the reading does not change as the switch is activated, replace the HVAC control module.
2. Ignition ON, observe the rear defogger switch indicator while turning the rear defogger switch ON and OFF. The indicator should turn ON and OFF as the switch is activated.
• If the rear defogger switch indicator does not illuminate, replace the HVAC control module.
Rear Window Defogger Malfunction
1. Ignition OFF, disconnect the rear defog relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal R8 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 relay switch B+ circuit terminal R7 and ground.
• If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay switch B+ circuit fuse is open, test the relay controlled output circuit terminal R8 for a short to ground.
4. Ignition ON, verify that a test lamp illuminates between the relay coil B+ circuit terminal R6 and ground.
• If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance.
5. Ignition OFF, disconnect the X1 harness connector at the rear window defogger grid.
6. Ignition OFF, all doors closed, test for less than 5.0 ohms of resistance between the rear window defogger grid ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the X1 harness connector at the rear window defogger grid.
8. Ignition OFF, disconnect the X2 harness connector at the rear window defogger grid.
9. Ignition OFF, all doors closed, test for less than 5.0 ohms of resistance between the rear window defogger grid ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
10. Connect the X2 harness connector at the rear window defogger grid.
11. Ignition ON, connect a 40 A fused jumper wire between the B+ circuit terminal R7 and the control circuit terminal R8. Verify the rear window defogger grid is activated.
• If the rear window defogger grid does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the rear window defogger grid.
12. Ignition OFF, connect a test lamp between the relay B+ circuit terminal R7 and the relay control circuit terminal R10.
13. Command the rear window defogger 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 ground. If the circuit tests normal, replace the RIM.
• 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 RIM.
14. If all circuits test normal, test or replace the rear defog relay.
Component Testing
Rear Window Defogger Grid Test
1. Ignition ON, turn on the rear defogger.
2. Verify that a test lamp illuminates between each rear 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 a grid line, test for an open between the test point and the ground circuit.
• If the test lamp remains off at the middle of a 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 (Verification Tests) after completing the diagnostic procedure.
* Rear Window Replacement (Rear Window Replacement)
* Relay Replacement (Attached to Wire Harness) (Relay Replacement (Attached to Wire Harness))Relay Replacement (Within an Electrical Center) (Relay Replacement (Within an Electrical Center))
* Control Module References (Programming and Relearning) for HVAC control module or RIM replacement, setup, and programming