Testing Rear Window Defogger Grid Line

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

1. Turn ignition ON. Turn rear window defogger on. From inside of vehicle, connect a voltmeter to each end of a grid line. Voltmeter will indicate battery voltage if grid line is open.
2. If a grid line is found to be open, move a voltmeter lead from one side of grid line and retest at a point nearer to other side of window. Continue to retest, each time bringing one of voltmeter leads closer to opposite side of window from where it was originally placed. Break in grid line is at point where voltmeter begins reading 0 volts instead of battery voltage.
3. Use a marking crayon to lightly mark break point on rear window. Mark glass instead of marking directly on grid line, and make mark far enough from grid line so that it can easily be removed without disturbing repair. Use a grid line repair kit to fix break in grid line.