Rear Window Defogger Malfunction
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
When the HVAC control module receives a rear window defog request from the rear window defogger switch, the HVAC control module will supply voltage to the relay coil. 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 to flow through the switch contacts and out the relay switched output to the rear 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. Ignition ON, observe the scan tool Rear Defog Relay parameter while pressing the rear window defogger switch. The parameter should change from Off to On.
• If the value does not change, replace the HVAC control module.
2. Command the rear window defogger ON and OFF with a scan tool, the rear defogger grid should turn ON or OFF while changing between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the KR5 rear defogger relay.
2. Test for less than 10 ohms 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 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 a test lamp illuminates between the B+ circuit terminal 87 and ground.
• If the test lamp does not illuminate and the B+ fuse is open, test the control circuit terminal 30 for a short to ground. If the circuit tests normal, test or replace the KR5 rear defogger relay.
5. Ignition OFF, disconnect the X2 harness connector at the E18 rear defogger grid.
6. Test for less than 5 ohms 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 E18 rear defogger grid.
8. Ignition ON, connect a 40 A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. Verify the E18 rear defogger grid is activated.
• If the E18 rear defogger grid does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the rear defogger grid.
9. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
10. 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 voltage. If the circuit tests normal, replace the K33 HVAC control module.
• 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 K33 HVAC control module.
11. If all circuits test normal, test or replace the KR5 rear defogger relay.
Component Testing
Rear Window Defogger Grid Test
1. Engine running, turn on the E18 rear defogger grid.
2. Verify that a test lamp illuminates between each E18 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 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 KR5 rear defogger relay.
2. Test for 60-180 ohms between terminals 85 and 86.
• If the not within the specified range, replace the KR5 rear defogger 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 KR5 rear defogger relay.
4. Install a 5 A fused jumper wire between relay terminal 85 and 12 V. 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 KR5 rear defogger relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Rear Window Replacement Rear Window Replacement
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Control Module References Control Module References for HVAC control module control replacement, programming and setup