Rear Window Defogger Function Test

NOTE: 

• Before testing, make sure the No. A2-8 (40 A) fuse in the under-hood fuse/relay box is OK.
• Before testing, make sure the No. B1 (7.5 A) fuse in the under-dash fuse/relay box is OK.
• Aftermarket window tinting should be removed before testing.
• When testing the defogger, hold a cup of hot steaming water near the glass. The steam can help diagnose a broken or under-performing defogger grid.
• Be careful not to scratch or damage the defogger wires with the tester probe. To avoid damaging the defogger grid, wrap a single strand of bare copper wire or aluminum foil around the voltmeter probe. Use the foil or wire as a contact brush when moving across the defogger grid.

Courtesy of HONDA, U.S.A., INC.

1. Turn the vehicle to the ON mode

2. Measure the voltage between the rear window defogger A (1P) positive terminal and body ground. There should be battery voltage.

• If there is no voltage, check for:
  • Faulty rear window defogger relay.
  • Faulty climate control switch.
  • Faulty climate control unit.
  • An open or high resistance in the GRN wire to the positive terminal.
• If there is battery voltage, go to step 3.

Courtesy of HONDA, U.S.A., INC.

3. Measure the voltage between the rear window defogger B (1P) negative terminal and body ground. There should be less than 0.2 V.

If there is more than 0.2 V, check for an open or high resistance in the ground (BLK) wire or poor ground (G601). If there is 0.2 V or less, go to step 4.

4. Touch the voltmeter positive probe along 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 voltage is more than specified at one of the points, there is a break or high resistance toward the negative half of the wire.
  • If voltage is less than specified at one of the points, there is a break or high resistance toward the positive half of the wire.