Detecting Breaks in Rear Window Defogger Grid

The horizontal grid lines and vertical bus bar lines printed and baked on inside surface of the window glass makes up an electrical parallel circuit. The electrically conductive lines are composed of a silver ceramic material which when baked on glass becomes bonded to the glass and is highly resistant to abrasion. It is possible, however, that a break may exist or 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. Turn ignition and rear window defogger control switch ON. The indicator light should come on.

Grid Line Test:

2. Using a DC voltmeter with 0-15 volt range, contact vertical bus bar connecting grid lines on passenger side of vehicle at terminal A with negative lead of voltmeter. With positive lead of voltmeter, contact vertical bus bar on driver side of vehicle at terminal B. The voltmeter should read 10-14 volts.
3. With negative lead of voltmeter, contact a good body ground point. The voltage reading should not change. A different reading indicates a poor ground connection.
4. Connect negative lead of voltmeter to terminal A on passenger side bus bar and touch each grid line at Mid-Point with positive lead. A reading of approximately 6 volts indicates a line is good. A reading of 0 volts indicates a break in line between Mid-Point C and terminal B. A reading of 10-14 volts indicates a break between Mid-Point C and ground terminal A. Move toward break and voltage will change as soon as break is crossed.