GM Bonneville/Eighty Eight/LeSabre 1986-1999

Rear Defogger System



A grid type heating element is affixed to the rear window, and an instrument panel mounted switch with an integral indicator lamp is used to turn the system ON. When the system is turned ON, a small electric current passes through the grid and its circuit, generating heat to clear the window. All rear defogger systems operate on 12 volts.

Certain conditions, such as outside temperature, vehicle speed, atmospheric pressure and even the number of passengers inside the vehicle, affect the length of time required to remove fog from the glass.

The defogger is designed to turn OFF after approximately 10 minutes of operation. If the defogger is turned ON again, it will only operate for approximately 5 minutes. You can, however, turn the system OFF before the time is up by turning the defogger switch or ignition switch OFF.


See Figure 1

  1. Start the engine and pull out the defogger switch knob.
  3. Using a test lamp, ground the end and touch the probe to each grid line. The test lamp should operate as indicated.
  5. If the test lamp remains bright at both ends of the grid lines, check for a loose ground.

The range zones may vary slightly from one glass to another, but the test lamp brilliance will decrease proportionately as it is moved from left to right on the grid line.

  1. If an abnormal reading is observed by the test lamp on any grid line, place the test lamp probe on the left of that bus bar and move the probe toward the right until the test lamp goes out. This will indicate a break in the continuity on that grid line.

Click image to see an enlarged view

Fig. Fig. 1: Use a test lamp to check the rear defogger for a broken grid


See Figures 2 and 3

  1. Locate the break(s) on the grid line(s) and mark the outside of the glass, using a grease pencil.
  3. Disconnect the negative battery cable.
  5. Clean the area to be repaired. Buff with steel wool and wipe clean with a damped cloth with alcohol.
  7. Position a strip of tape above and below the grid line area to be repair.
  9. Repair the grid line break using defogger repair kit (Part 1052858 or equivalent) and follow the manufacturer's instructions.

Click image to see an enlarged view

Fig. Fig. 2: Apply the repair material to the broken grid wire

  1. After the grid line has been repaired, carefully remove the strips of tape.
  3. Apply heat, using a heat gun, to the repaired area for approximately 1-2 minutes. A minimum temperature of 300°F (149°C) is required.

Click image to see an enlarged view

Fig. Fig. 3: Use a heat gun to dry the repair. Be careful NOT to overheat the glass

To avoid damage to the interior trim, protect the trim near the area to be repair. Allow the repair materials to cure for at least 24 hours. Do not operate the unit until such time.

  1. Test the rear defogger operation to verify proper operation.