Locate inoperative grid lines by starting the engine and turning on the rear window defogger system. Ground one test lamp lead (probe) and lightly touch the other probe to each grid line. Refer to the pattern of test lamp brilliance to be expected with a properly functioning grid. If test lamp bulb shows full brilliance at both ends of grid lines, inspect for loose ground wire contact to body metal.

The locations on the graphic are identified by the following key:

1. Full bulb brilliance (1)
2. Three quarters bulb brilliance (2)
3. One half bulb brilliance (3)
4. One quarter bulb brilliance (4)
5. No bulb brilliance (5)

The range of zones may vary slightly from one window to another. The bulb brilliance will decrease proportionately to the increased resistance in the grid line as the probe is moved from the left bus bar to the right. Test all grid lines in at least two places in order to eliminate the possibility of bridging a break. For best results, contact each grid line a few millimeters on either side of the window centerline. If an abnormal light reading is apparent on a specific grid line, place test lamp probe on that grid at the left bus bar and move the probe toward the right bus bar until the light goes out. This will indicate a break in the continuity of the grid line.

The locations on the graphic are identified by the following key:

1. No light
2. Broken grid
3. Full brilliance
4. Full brilliance
5. Feed bus bar
6. Ground bus bar