For 1990-2009 cars

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 are operating, a full system diagnosis should be completed before attempting to repair the grid lines.

1. Turn the ignition ON.
2. Turn the rear window defogger ON.

Caution: Use extreme care when testing the rear window defogger grid line using a DMM. The test lead from the DMM if applied to roughly to the grid line could cause an open circuit.

3. From the inside of the vehicle, connect a voltmeter to each end of a grid line. The voltmeter will indicate battery voltage if the grid line is open.
4. If a grid line is found to be open, repair as necessary.