Defogger System Testing

Defogger System
Electrically heated defogger operation can be confirmed in one of the following manners:
1. Turn the ignition switch to the On position. While monitoring the instrument panel voltmeter, set the defogger switch in the On position. When the defogger switch is turned On, a distinct voltmeter needle deflection should be noted.
2. Turn the ignition switch to the On position. Set the defogger switch in the On position. The rear window defogger operation can be checked by feeling the glass. A distinct difference in the temperature between the grid lines and the adjacent clear glass can be detected within three to four minutes of operation.

Rear Window Glass Grid Test:

3. Using a 12-volt DC voltmeter, contact the rear glass heating grid terminal A (passenger side) with the negative lead, and terminal B (driver side) with the positive lead. The voltmeter should read battery voltage.

The above checks will confirm system operation. Illumination of the switch indicator lamp means that there is electrical current available at the output of the defogger switch module, but does not confirm
that the electrical current is reaching the rear glass heating grid lines.

If the defogger system does not operate, the problem should be isolated in the following manner:
1. Confirm that the ignition switch is in the On position.
2. Ensure that the rear glass heating grid feed and ground wires are connected to the glass. Confirm that the ground wire has continuity to ground, and that there is continuity between the electrical contacts in the rear door hinge pillar when the rear door is closed.
3. Check the fuses in the Power Distribution Center and in the fuseblock module. The fuses must be tight in their receptacles and all electrical connections must be secure.

When the above steps have been completed and the rear glass heating grid is still inoperative, one or more of the following is faulty:
- Defogger switch, relay, and timer module
- Rear window grid lines (all grid lines would have to be broken or one of the feed wires disconnected for the entire system to be inoperative).

If setting the defogger switch to the On position produces a severe voltmeter deflection, check for a short circuit between the defogger switch module and the rear glass heating grid.

Rear Glass Heating Grid
To detect breaks in the grid lines, the following procedure is required:
1. Turn the ignition switch to the On position. Set the defogger switch in the On position. The indicator lamp should light. If OK, go to Step 2. If not OK, see the Defogger Switch, Relay, and Timer Module diagnosis.
2. Using a 12-volt DC voltmeter, contact the vertical bus bar on the passenger side of the vehicle with the negative lead. With the positive lead, contact the vertical bus bar on the driver side of the vehicle. The voltmeter should read battery voltage. If OK, go to Step 3. If not OK, repair the open circuit to the defogger switch as required.
3. With the negative lead of the voltmeter, contact a good body ground point. The voltage reading should not change. If OK, go to Step 4. If not OK, repair the circuit to ground as required.
4. Connect the negative lead of the voltmeter to the passenger side bus bar and touch each grid line at mid-point C with the positive lead. A reading of approximately six volts indicates a line is good. A reading of zero volts indicates a break in the grid line between mid-point C and the driver side bus bar. A reading of ten to fourteen volts indicates a break between mid-point C and the passenger side bus bar. Move the positive lead on the grid line towards the break and the voltage reading will change as soon as the break is crossed.