Caution: Refer to Avoid Damage to Grid Lines Caution in the Preface section.

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

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, move a voltmeter terminal from one side of the grid line and retest at a point nearer to the other side of the window. Continue to retest, each time bringing one of the voltmeter terminals closer to the opposite side of the window from where it was originally connected. The break in the grid line is at the point where the voltmeter begins reading 0 volts instead of battery voltage.
5. Use a marking crayon to lightly mark the break point on the rear window. Mark the glass instead of marking directly on the grid line, and make the mark far enough from the grid line so that the mark can easily be removed without disturbing the repair.
6. Use a grid line repair kit to fix the break in the grid line. Refer to Grid Line Repair.