When you depress the rear defogger switch, 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.

When you turn ON the ignition and press the rear window defogger switch for the first time, the defogger cycle lasts 15 minutes. Further operation results in 7.5 minute defogger cycles.

Schematic Reference

Defogger Schematics

Connector End View Reference

Window Systems Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

Ignition ON, command the rear window defogger ON and OFF by pressing the defog button. Observe the rear window defogger operation as the rear window defogger turns ON and OFF.

1. Ignition OFF, disconnect the harness connector C3 at the HVAC control assembly.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal C and ground.

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

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

⇒	If the test lamp does not illuminate, test the RUN circuit for a short to ground or an open/high resistance. If the circuit test normal and the HTR/AC circuit breaker or fuse is open, replace the HVAC control assembly.

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 RR DEFOG fuse is open, test the control circuit terminal D for a short to ground.

5. Ignition OFF, connect the harness connector C3 at the HVAC control assembly
6. Disconnect the harness connector C2 at the defogger grid
7. Test for less than 1.0 ohm of resistance between the defogger grid ground circuit terminal A and ground.

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

8. Disconnect C1 and connect a test lamp between the control circuit terminal A and ground.
9. Ignition ON, command the rear window defogger ON and OFF by pressing 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 HVAC control assembly.

⇒	If the test lamp is always OFF and the RR DEFOG fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control assembly.

⇒	If the test lamp is always OFF and the RR DEFOG fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the defogger grid.

10. If all circuits test normal, test or replace the defogger grid.

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.