When the rear defogger switch is pressed, voltage is supplied to the defogger grid and the HVAC control assembly also illuminates the rear window defogger indicator. The HVAC control assembly contains a printed circuit board (PCB) relay, which when commanded by the HVAC control assembly, provides battery positive voltage from the relay to the rear window 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

Ignition ON, observe the operation of the rear window defogger and the rear window defogger indicator while pressing the rear window defogger switch. The rear window defogger and rear window defogger indicator should turn ON and OFF each time the rear window defogger switch is pressed.

1. Ignition OFF, disconnect the X3 harness connector at the HVAC control assembly.
2. Test for less than 1 ohm between the ground circuit terminal C and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal B and ground.

⇒	If the test lamp does not illuminate, test the igniton circuit for a short to ground or an open/high resistance.

4. Verify that 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 B+ circuit fuse is open, test the control circuit terminal D for a short to ground. If the circuit tests normal, replace the HVAC control assembly.

5. Ignition OFF, disconnect the X2 harness connector at the defogger grid.
6. Test for less than 1 ohm between the ground circuit terminal A and ground.

⇒	If greater than the specified value, test the ground circuit for an open/high resistance.

7. Connect the X2 harness connector at the rear window defogger grid.
8. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal A and the control circuit terminal D, 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.

9. If all circuits test normal, HVAC control assembly.

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.