Window Defogger Function Test

The electrically heated rear window defogger operation can be checked on the vehicle in the following manner:

1. Turn the ignition switch to the On position.
2. Make sure that the defogger switch is Off.
3. Using a ammeter on the battery, turn the rear defogger control switch to the On position, a distinct increase in amperage draw should be noted.
4. The rear window defogger operation can be checked by feeling the glass. A distinct difference in temperature between the grid lines and adjacent clear glass should be detected in three to four minutes of operation.

Grid Line Test:

5. Using a DC voltmeter, contact the negative lead to Point B, and the positive lead to Point A. The voltmeter should read 10-14 volts.

NOTE: Illumination of the LED indicator means that there is power available at the switch, but does not necessarily verify system operation.

6. If turning the defogger switch On produced no distinct current draw on the ammeter, the problem should be isolated in the following manner:
- Confirm that the ignition switch is On.
- Make sure that the heated rear window feed wire is connected to the terminal and that the ground wire is in fact grounded.
- Make sure that fuse 13 (40 amp) in the integrated power module (IPM) is OK.

7. When the above steps have been completed and the system is still inoperative, one or more of the following could be defective. It may be necessary to connect a DRBIII(R) scan tool to perform further diagnostics. Refer to Body Diagnostic Procedures.
- Rear window defogger switch in the A/C-heater control.
- J1850 bus communication between the A/C-heater control and the front control module (FCM).
- Rear window defogger relay in the IPM.
- Rear window defogger relay control circuity in the IPM.
- Check for a loose wire connector or a wire pushed out of a connector.
- Rear window grid lines (all grid lines would have to be broken, or one of the feed wires not connected for the system to be inoperative).

8. If turning the rear window defogger switch On produces severe voltmeter deflection, the circuit should be closely checked for a shorting condition.
9. If the system operation has been verified but LED indicator does not illuminate, replace the A/C-heater control.
10. For detailed wiring information, refer to Wiring Diagrams.