Heated Glass Element: Testing and Inspection

Electrically heated rear window defogger operation can be checked in vehicle in the following manner:
1. Turn ignition switch to the ON position.
2. Connect an ammeter in series with the battery. Push the defogger control switch to the ON position. A distinct increase in amperage draw should be noted.
3. 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 three to four minutes of operation.




4. Using a DC voltmeter, connect negative lead to Point B, and the positive lead to Point A. The voltmeter should read 10-14 volts.
5. Step 2, Step 3 or Step 4 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.
6. 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 maxi-fuse and control circuit fuse are OK and all electrical connections are secure.
7. When the above steps have been completed and the system is still inoperative, one or more of the following is defective:
a. Control switch/timer relay module.
b. rear window grid lines would have to be broken or one of the feed wires are not connected for the system to be inoperative.
8. If turning the 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 indicator lamp does not light, replace the switch.

Grid Lines
The horizontal grid lines and vertical bus bar lines printed and fired on inside surface of rear window glass comprise an electrical parallel circuit. The electrically conductive lines are composed of a silver-ceramic material which when fired on glass becomes bonded to the glass and is highly resistant to abrasion. It is possible, however, that a break may 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 ON and turn control switch to ON. The indicator light should come on.
2. Using a DC voltmeter with 0-15 volt range, contact terminal B with negative lead of voltmeter. With positive lead of voltmeter, contact terminal A. The voltmeter should read 10-14 volts. A lower voltage reading indicates a poor connection in the feed or the ground circuit.
3. With negative lead of voltmeter, contact a good body ground point. The voltage reading should not change.
4. Connect negative lead of voltmeter to terminal B and touch each grid line at Mid-Point with Positive lead. A reading of:
- Approximately 6 volts indicates the line is OK
- 0 volts indicates a break in line between Mid-Point C and terminal A
- 10-14 volts indicates a break between Mid-Point C and terminal B

Systems Electrical Circuit:

Move the lead toward the break and voltage will change as soon as break is crossed.