Defogger System Testing

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, 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 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 fuse 12 (EBL) in the Power Distribution Center is OK.
8. 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.
9. If depressing the switch button ON produces severe voltmeter deflection, the circuit should be closely checked for a shorting condition.
10. 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.

Grid Line Test

Grid Line Test:

The horizontal grid lines and vertical bus bar lines printed and baked on inside surface of the window glass makes up an electrical parallel circuit. The electrically conductive lines are composed of a silver ceramic material which when baked on glass becomes bonded to the glass and is highly resistant to abrasion. It is possible, however, that a break may exist or occur in an individual grid line resulting in no current flow through the line. To detect breaks in grid lines, the following procedure is required:
1. Turn ignition and rear window defogger control switch ON. The indicator light should come on.
2. Using a DC voltmeter with 0 - 15 Volt range, contact vertical bus bar connecting grid lines on passenger side of vehicle at terminal A with negative lead of voltmeter. With positive lead of voltmeter, contact vertical bus bar on driver side of vehicle at terminal B. The voltmeter should read 10 - 14 Volts.
3. With negative lead of voltmeter, contact a good body ground point. The voltage reading should not change. A different reading indicates a poor ground connection.
4. Connect negative lead of voltmeter to terminal A on passenger side bus bar and touch each grid line at Mid-Point with positive lead. A reading of approx 6 Volts indicates a line is good. A reading of 0 Volts indicates a break in line between Mid-Point C and terminal B. A reading of 10 - 14 Volts indicates a break between Mid-Point C and ground terminal A. Move toward break and voltage will change as soon as break is crossed.