Heated Glass Element: Testing and Inspection
Rear Window Defogger Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Battery positive voltage is supplied through a 30A fuse in the underhood fuse block, to the rear defogger relay switched input. When the rear window defogger switch is pressed, The HVAC control module commands the rear window defogger system by supplying voltage to the rear defogger relay coil. The rear defogger relay is energized and the defogger indicator is illuminated. With the relay energized, battery positive voltage is allowed from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid.
Reference Information
Schematic Reference
Defogger Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Description and Operation
Rear Window Defogger Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Engine running.
2. Verify the scan tool Rear Defogger Switch parameter changes between Active and Inactive when pressing the rear window defogger switch.
• If the parameter does not change between Active and Inactive
Replace the K33 HVAC control module.
• If the parameter changes between On and Off
3. Verify the E18 Rear Defogger Grid turns ON and OFF when pressing the rear window defogger switch.
• If the E18 Rear Defogger Grid does not turn ON and OFF
Refer to Circuit/System Testing
• If the E18 Rear Defogger Grid turns ON and OFF
4. Verify the rear window defog indicator turns ON and OFF when pressing the rear window defogger switch.
• If the rear window defog indicator does not turn ON and OFF
Replace the K33 HVAC control module.
• If the rear window defog indicator turns ON and OFF
5. All OK.
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the KR5 Rear Defogger Relay. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 85 and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
3. Engine running.
4. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
5. Verify the test lamp turns ON and OFF when pressing the rear window defogger switch.
• If the test lamp is always OFF
1. Ignition OFF, disconnect the harness connector at the K33 HVAC control module.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K33 HVAC control module.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the K33 HVAC control module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K33 HVAC control module.
• If the test lamp turns ON and OFF
6. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
• If the test lamp illuminates
Repair the short to voltage on the control circuit
• If the test lamp does not illuminate
7. Ignition OFF and all vehicle systems OFF, disconnect the X2 harness connector at the E18 Rear Defogger Grid. It may take up to 2 minutes for all vehicle systems to power down.
8. Test for less than 10 ohms between the ground circuit terminal A and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
9. Connect the X2 harness connector at the E18 Rear Defogger Grid.
10. Ignition ON, connect a 30 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
11. Verify the E18 Rear Defogger Grid is activated.
• If the E18 Rear Defogger Grid does not activate
1. Ignition OFF, disconnect the X1 harness connector at the E18 Rear Defogger Grid.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the E18 Rear Defogger Grid.
• If the E18 Rear Defogger Grid activates
12. Test or replace the KR5 Rear Defogger Relay.
Component Testing
Relay Test
1. Ignition OFF, disconnect the KR5 Rear Defogger Relay.
2. Test for 60-180 ohms between terminals 85 and 86.
• If less than 60 ohms or greater than 180 ohms
Replace the KR5 Rear Defogger Relay.
• If between 60-180 ohms
3. Test for infinite resistance between the terminals listed below:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less than infinite resistance
Replace the KR5 Rear Defogger Relay.
• If infinite resistance
4. Install a 3 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground.
5. Test for less than 2 ohms between terminals 30 and 87.
• If 2 ohms or greater
Replace the KR5 Rear Defogger Relay.
• If less than 2 ohms
6. All OK
Rear Defogger Grid Test
Note: Lightly touch the grid lines when testing with the test lamp. If the test lamp point is scraped through the grid line it can cause an open in the circuit
1. Engine running, command the Rear Defogger ON with a scan tool.
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.
The grid line is open between the test point and the ground side of the grid.
Replace the rear window
• If the test lamp remains off at the middle of the grid line.
The grid line is open between the test point and the voltage supply side of the grid.
Replace the rear window
• If the test lamp remains dim at the middle of each grid line.
3. All OK
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Rear Window Replacement Rear Window Replacement
* Liftgate Window Replacement Service and Repair
* Control Module References Control Module References for HVAC control module replacement, programming and setup