Window Defogger System Test

Electrically heated rear window defogger operation can be checked in vehicle in the following manner:
1. Turn ignition switch to the ON position.
2. Make sure defogger switch is OFF.
3. Remove the battery negative remote cable from the terminal. Using a ammeter (capable of a 30 AMP range), connect the ammeter is series between the battery cable and the remote terminal. Turn the Defogger control switch ON, 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 can be detected in 3 to 4 minutes of operation.

Grid Line Test:

5. Using a DC voltmeter contact terminal B with the negative lead, and terminal A with the positive lead. The voltmeter should read 10 - 14 volts.
6. Step 3, Step 4, and Step 5 above will confirm system operation. Indicator light illumination means that there is power available at the output of the relay only, and does not necessarily verify system operation.
7. If the indicator light is not ON, then check fuse #6 in the junction block.
8. If turning the switch ON produced no distinct current draw on the ammeter the problem should be isolated in the following manner:
a. Confirm the ignition switch is ON.
b. Ensure that the heated rear glass feed wire is connected to the terminal or pigtail and that the ground wire is in fact grounded.
c. Ensure that the 40 amp EBL fuse in the Power Distribution Center is OK.
9. when the above steps have been completed and the system is still inoperative, one or more of the following is defective:
a. Control switch in the HVAC control module
b. Rear window defogger relay (EBL) in the Junction Block
c. Timer circuit in the Body Control Module
d. Rear window grid lines, all grid lines would have to be broken or one of the feed wires are not connected for the system to be inoperative.
10. If depressing the switch button ON produces severe voltmeter deflection, the circuit should be closely checked for a shorting condition.
11. If the system operation has been verified but indicator bulb does not light, check fuse 6 in the junction block. If not OK, replace as necessary If OK, test the HVAC control module.
12. For detailed wiring information, refer to Wiring Diagrams.