Component Tests and General Diagnostics
TOOLS REQUIREDJ 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.