Tools Required

J 39200 Digital Multimeter

In order to locate inoperative grid lines, start the engine and turn on the rear window defogger system. Ground the negative lead of the J 39200 . Lightly touch the positive lead to each grid line. Voltage will decrease as the lead is moved farther away from the feed bus bar. If the J 39200 shows a high voltage at both ends of the grid lines, inspect for a loose ground terminal-to-bus bar connection or a loose ground wire-to-body connection.

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 meter reading is apparent on a specific grid line, place the lead on that grid line and move the lead until the voltage drops significantly. A drop in voltage indicates a break in the continuity of the grid line. Use a wax pencil or a crayon in order to mark the grid line breaks on the outside of the window.