Window Defogger Grid Lines Test

The horizontal grid line and vertical bus bar line is printed and fired on the inside surface of the rear window glass. These comprise an electrical circuit. The electrically conductive lines are composed of a silver ceramic material which when fired on glass becomes bonded to the glass and is highly resistant to abrasion. It is possible, however, that a break may occur in an individual grid line resulting in no current flow through the line. To detect breaks in grid lines, the following procedure is required:
1. Stop the engine. Connect the negative lead of a 0 - 25 volt range voltmeter to a known good vehicle electrical ground.
2. Start the engine and push the rear window defogger button to turn on the system.

Fig.4 Grid Line Test:

3. Touch the ground side (point B) of the Rear Window Defogger Grid. The voltage measured should be below 1 volt. If the voltage is greater than 1 volt then check the voltage on each grid line at the Mid-Point with the positive lead. If the voltage is not approximately 6 volts or half the voltage measured on the positive rear window grid bus bar, then the grid line is bad. The break in the grid can be found by moving the probe along the line until the voltage changes. The area where the voltage changes is where the open circuit is.