Rear Window Defogger Function Test

  • Be careful not to scratch or damage the defogger wires with the tester probe.
  • Before testing, check the No. 9 (20A) fuse in the under-dash fuse/relay box.

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

  • If there is no voltage, check for:
    • an open in the wire between the defogger switch and positive terminal.
    • faulty the defogger switch
  • If there is battery voltage, go to 2.


2.Check for continuity between the negative terminal (B) and body ground.
If there is no continuity, check for:
  • an open in the BLK wire.
  • Poor ground (G602)

3.Touch the voltmeter positive probe to the halfway point of each defogger wire, and the negative probe to the negative terminal.
There should be about 6 V with the ignition switch and the defogger switch ON.

  • If the voltage is as specified, the defogger wire is OK.
  • If the voltage is not as specified, repair the defogger wire.
    • If it is more than 6 V, there is a break in the negative half of the wire.
    • If it is less than 6 V, there is a break in the positive half of the wire.