Rear Window Defogger Function Test


1.Check for voltage between the positive terminal (A) and body ground with the ignition switch and the defogger switch ON.
There should be battery voltage.

  • If there is no voltage, check for:
    • Faulty rear window defogger relay.
    • Faulty climate control unit/HVAC control unit/heater control panel.
    • An open in the RED wire to the positive terminal.
  • If there is voltage, go to 2.


2.Disconnect the negative terminal (B) from the rear window defogger.

3.Check for continuity between the negative terminal (B) and body ground.

If there is no continuity, check for an open in the wire or poor ground (G801). If there is continuity, go to 4.

4.Reconnect the negative terminal to the rear window defogger.

5.Turn the ignition switch ON (II) and the rear window defogger switch ON.

6.Touch the voltmeter positive probe to each point on each defogger wire, and the negative probe to the negative terminal.

  • If the voltage is as specified, the defogger wire up to that point is OK.
  • If the voltage is not as specified, repair the defogger wire.
    • If it is more than specified at one of the points, there is a break in the negative half of the wire.
    • If it is less than specified at one of the points, there is a break in the positive half of the wire.