Defogger Grid Lines Diagnosis

Defogger Grid Lines Diagnosis

If it has been observed during use that a grid line is inoperative, the following procedure can be used to find the break. If none of the grid lines is operating, a full system diagnosis should be completed before attempting to repair the grid lines.

1. Engine Running.

2. Turn ON the rear window defogger.

Note: The first place to check should be the driver side segment 2 to 3 lines up from the bottom about 380-385 mm (15-15.2 in) from buss bar

3. Take the ball of fine steel wool and twist one end to a point. Move the point slowly across each grid line. Be sure to start at the far side of the zone and move it to the opposite side of the zone. When you bridge the grid line break with the steel wool, you will see a small spark. Repeat the test over the same area to be sure you have accurately located the break. Mark the exact location of the grid line break. Repeat this portion of the test for each grid line. If you do not see a spark at any point, it is possible that there are two breaks in the same line and zone. Close visual inspection using a magnifying glass may be the only way to locate breaks in this case.

4. The following are provided as a alternative way to detect a non-functional grid line. If available, use in addition to the steel wool.

1. Method using liquid crystal heat sensitive paper:

Note: The first part of the test must be completed quickly before the entire surface of the back window becomes warm

1. From outside the vehicle, place the heat sensitive paper (dull surface in contact with the glass) against the top driver side grid line. Start the engine and turn on the back window defogger. A distinct color change will take place at each conductive grid line. Repeat for the bottom grid lines until they have all been checked in the driver side zone.

2. Repeat the process for the passenger side and center area zones

3. If no color change is noted for a grid line, place a crayon or china marker check mark beside it. Mark each grid line in the zone where it is non-conductive and therefore not heating up. More than one broken grid line may be found.

2. Method using a portable infrared thermometer

1. Start the engine and turn on the rear back window defogger

2. From inside the vehicle, start at the top driver side grid line and slowly run the portable infrared thermometer vertically down the rear window contacting each grid line. You should be able to see a district variation in temperature readings

3. Mark each grid line in the zone where it is non-conductive and, therefore, not heating up. More than one broken grid line may be found

4. Repeat the process for the passenger side and center area zones

5. If a broken defogger grid is detected, the recommended repair is rear window replacement.