The rear window defogger switch and indicator is an integral component of the HVAC control module. When the rear window defogger switch is pressed, the HVAC control module responds by illuminating the defogger indicator and sending a serial data message indicating a defog request. This serial data message is received by the liftgate module (LGM). The LGM responds to the defog request by providing voltage to the rear window defogger grid. Pressing the rear window defogger switch again will turn off the indicator and send a serial data message indicating the defog deactivation command. The LGM responds by deactivating the defogger grid.

Schematic Reference

Defogger Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool Rear Defrost Switch parameters while pressing the rear window defogger switch. The parameter should change between On and Off.

⇒	If the parameter does not change between commanded states, replace the HVAC control module.

2. Observe the operation of the rear window defogger indicator while pressing the rear window defogger switch. The indicator should turn ON or OFF each time the rear window defogger switch is pressed.

⇒	If the indicator does not turn ON or OFF with each switch press, replace the HVAC control module

3. Command the Rear Defog ON and OFF with a scan tool. The rear window defogger should turn ON and OFF when changing between the commanded states.

1. Ignition OFF, disconnect the X1 harness connector at the LGM
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal A and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the LGM #2 fuse is open, replace the LGM.

3. Ignition OFF, connect the X1 harness connector at the LGM and disconnect the X1 and X2 harness connectors at the rear window defogger grid.
4. 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.

5. Connect a test lamp between the control circuit terminal A and ground.
6. Ignition ON, command the Rear Defog 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 LGM.

⇒	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 LGM.

7. If all circuits test normal, test or replace the rear window defogger.

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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.