This test is for reference only. A grid line fault requires the rear window replacement. Refer to Rear Window Replacement .

Opens in the grid lines of the rear window defogger can cause symptoms such as poor clearing of the rear window or crackling noise on the AM radio stations when the rear window defogger is ON. If a grid line is open, that grid line will not heat which means the glass area around that grid line will not clear. Some of these opens are very small and are consider microcracks. Microcracks cause noise in the radio stations by the voltage arching across the gap of the microcrack. This arching is picked up by the radio antenna made on the rear glass or by a system where the rear window defogger is used as an radio antenna. Refer to one of the procedures below that properly addresses the concern.

1. Start the engine.
2. Activate the rear window defogger system.
3. Connect a test lamp to a good ground.




Important: The test lamp brilliance will decrease proportionately to the increased resistance in the grid line as the probe is moved from the battery positive bus wire to the ground bus wire. The test lamp brilliance may vary from one window to another.

4. Move the test lamp probe from zone 5 to zone 1 along each grid line.

•	If the test lamp does not illuminate, the rear defogger system may be inoperative. Refer to Rear Window Defogger Inoperative to properly diagnose this concern.

•	If the test lamp shows full brilliance at both ends of the grid lines. Inspect for an open or poor connection in the ground circuit of the rear window defogger grid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.





•	If the test lamp goes out, test the grid line in at least 2 places (1,3) to eliminate the possibility of bridging the open (2) in the grid line.

5. Once the open (2) is located, replace the rear window. Refer to Rear Window Replacement .

Important: Only use this procedure for rear window defogger systems that have the radio antenna made on the rear glass or where the rear window defogger is being used as a radio antenna.

1. Start the engine.
2. Turn the radio to a good AM radio station.
3. Activate the rear window defogger system.
4. If crackling noise is heard on the station when the rear window defogger is activated, replace the rear window. Refer to Rear Window Replacement .