Defogger Grid Lines Diagnosis
TOOLS REQUIREDJ 39200 Digital Multimeter
In order to locate inoperative grid lines, perform the following steps:
1. Start the engine.
2. Turn ON the rear window defogger system.
3. Ground the negative (-) lead of a J 39200. Lightly touch the positive (+) lead to each grid line (4).
Voltage will decrease as the lead is moved farther away from the feed bus bar (2).
If the J 39200 shows high voltage at both ends of the grid lines, test for loose ground connections at the following locations:
^ Ground terminal to bus bar
^ Ground wire to body
Test all of the grid lines in at least 2 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 meter reading is apparent on a specific grid line, place the lead on that grid. Move the lead until the voltage drops significantly. This procedure will indicate a break in the continuity of the grid line. Mark the grid line breaks on the outside of the window using a wax pencil or a crayon. Refer to Defogger Schematics for electrical diagnosis of the rear window defogger system.