Rear Defogger: Testing and Inspection

NOTE:
- Illumination of the defogger switch indicator lamp means that there is electrical current available at the output of the rear window defogger logic circuitry, but does not confirm that the electrical current is reaching the rear glass heating grid lines.
- For circuit descriptions and diagrams of the rear window defogger system.

Operation of the electrical backlight (EBL) system can be confirmed by the following:




1. Using a scan tool, check for diagnostic trouble codes (DTCs) related to the A/C-heater control and the front control module (FCM). If no DTCs are found, go to Step 2. If any DTCs are found, repair as required, then proceed to Step 2
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 rear window or outside rear view mirror glass. A distinct difference in temperature between the grid lines (4 and 5) and the adjacent clear glass or the mirror glass can be detected within three to four minutes of operation.
3. If a temperature difference is not detected, use a 12-volt DC voltmeter and contact the rear glass heating grid terminal A (1) with the negative lead, and terminal B (2) with the positive lead. The voltmeter should read battery voltage. If the voltmeter does not read battery voltage, check the following:
- Confirm that the ignition switch is in the On position.
- Make sure that the rear glass heating grid feed wire (3) and ground wire (6) are connected to the terminals. Confirm that the ground wire has continuity to ground.
- Check the EBL relay and fuse located in the junction block (JB). The relay and fuse must be tight in their receptacles and all electrical connections must be secure.
- Check the fuse located in the power distribution center (PDC). The fuse must be tight in its receptacle 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:
- Rear window defogger control switch in the A/C-heater control.
- Rear window defogger grid lines (all grid lines would have to be broken, or the power feed or the ground wire disconnected, for the entire heating grid to be inoperative).