Window Defogger System Control Test

For circuit descriptions and diagrams, refer to Rear Window Defogger in Wiring Diagrams.

WARNING: ON VEHICLES EQUIPPED WITH AIRBAGS, DISABLE THE AIRBAG SYSTEM BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE, THEN WAIT TWO MINUTES FOR THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE BEFORE PERFORMING FURTHER DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.


Rear Window Defogger System Control Test
1. Check the fuses in the fuse block module and the Power Distribution Center (PDC).
If OK, go to Step 2.
If not OK, repair the shorted circuit or component as required and replace the faulty fuse.

2. Check for battery voltage at the fused B(+) fuse in the PDC.
If OK, go to Step 3.
If not OK, repair the open circuit to the battery as required.

3. Turn the ignition switch to the ON position. Check for battery voltage at the fused ignition switch output (run) fuse in the fuse block module. If OK, go to Step 4. If not OK, repair the open fused ignition switch output (run) circuit to the ignition switch as required.

4. Disconnect and isolate the battery negative cable. Remove the heater and air conditioner control from the instrument panel. Refer to Heater-A/C Control in the Removal and Installation of Heating and Air Conditioning for the procedures. Unplug the 4-way rear window defogger switch wire harness connector from the control. Check for continuity between the ground circuit cavity of the rear window defogger switch wire harness connector and a good ground. There should be continuity.
If OK, go to Step 5.
If not OK, repair the open circuit to ground as required.

5. Connect the battery negative cable. Check for battery voltage at the fused B(+) circuit cavity of the rear window defogger switch wire harness connector.
If OK, go to Step 6.
If not OK, repair the open circuit to the fuse in the PDC as required.

6. Turn the ignition switch to the ON position. Check for battery voltage at the fused ignition switch output (run) circuit cavity of the rear window defogger switch wire harness connector.
If OK, go to Step 7.
If not OK, repair the open fused ignition switch output (run) circuit to the fuse in the fuse block module as required.

7. Turn the ignition switch to the OFF position. Disconnect and isolate the battery negative cable. Reconnect the 4-way rear window defogger switch wire harness connector to the heater and air conditioner control. Connect the battery negative cable. Turn the ignition switch to the ON position. Depress and release the rear window defogger switch. The amber rear window defogger indicator lamp above the switch button should light.
If OK, go to Step 8.
If not OK, replace the faulty heater and air conditioner control assembly

8. Back probe the rear defogger relay output circuit cavity of the rear window defogger switch wire harness connector and check for battery voltage.
If OK, see Rear Glass Heating Grid in the Diagnosis and Testing.
If not OK, replace the faulty heater and air conditioner control assembly.