In order to locate inoperative grid lines, complete the following steps:

1. Start the engine.
2. Turn ON the rear window defogger system.
3. Ground 1 test lamp lead.
4. Lightly touch the other lead to each grid line.
5. The illustration shows the pattern of test lamp brilliance that you may expect with a properly functioning grid.
6. If the test lamp bulb shows full brilliance at both ends of the grid line, inspect for a loose ground wire contact to the body metal.
7. The range of zones in the illustration may vary slightly from one window to another. However, the bulb brilliance will decrease proportionately to the increased resistance in the grid lines as you move the lead from the left bus bar to the right.

Test all of the grid lines in at least 2 places in order to eliminate the possibility of bridging a break. Test each grid line a few millimeters from the center of the window.

If abnormal test lamp brilliance is apparent on a specific grid line complete the following steps:

1. Place 1 of the leads on the grid at the left bus bar.
2. Move the other lead toward the right bus bar until the brilliance decreases significantly.

Decreasing brilliance on the test lamp indicates a break in the continuity of the grid line. Refer to Defogger and Heated Mirrors in Electrical Diagnosis for the electrical diagnosis of the rear window defogger system.