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Rear Window Defogger Relay Test

  1. Press control switch off. Using scan tool, select BODY, then TEMP CONTROL. Select INPUTS/OUTPUTS. Read REAR DEFOG SW status. If scan tool displays OPEN, go to next step. If scan tool does not display OPEN, replace A/C-heater control head.
  2. Push and hold control switch in ON position. Read REAR DEFOG SW status. If scan tool displays CLOSED, go to next step. If scan tool does not display CLOSED, replace A/C-heater control head.
  3. Turn ignition off. Using an external ohmmeter, backprobe between ground and bus bar ground "B" terminal on defogger grid. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open ground circuit to rear window defogger.
  4. Turn ignition on. Press control switch on. Using an external voltmeter, backprobe between ground and bus bar voltage feed "A" terminal on defogger grid. If voltage is more than 10 volts, repair defogger grid. See GRID FILAMENT REPAIR  under ON-VEHICLE SERVICE. If voltage is 10 volts or less, go to next step.
  5. Remove rear window defogger relay. See REAR WINDOW DEFOGGER RELAY  under REMOVAL & INSTALLATION. Using an external voltmeter, measure voltage between ground and relay connector terminals No. 2 and 5 (Black/Pink wires). See Figure . If voltage is 10 volts or less at either terminal, go to step  10 . If voltage is more than 10 volts on both terminals, go to next step.
    6. CAUTION: DO NOT leave jumper wire connected for a long period of time.
  6. Connect a jumper wire between rear defogger relay connector terminals No. 1 (Black/White wire) and either No. 2 or 5 (Black/Pink wires). Backprobe between ground and voltage feed "A" terminal on defogger grid. If voltage is 10 volts or less, disconnect jumper wire and repair open voltage feed "A" terminal (Black/White wire) circuit. If voltage is more than 10 volts, disconnect jumper wire and go to next step.
  7. Connect a test light between rear defogger relay connector terminals No. 2 (Black/Pink wire) and No. 4 (Dark Blue/White wire). Ensure rear defogger is on. If test light illuminates, replace rear defogger relay. If test light does not illuminate, go to next step.
  8. Turn ignition off. Disconnect Body Control Module (BCM) Blue connector. BCM is mounted to junction block located behind left end cap of instrument panel. Connect jumper wire between ground and BCM Blue connector terminal No. 14 (Dark Blue/White wire). See Figure . Go to next step.
  9. Using external ohmmeter, measure resistance between ground and rear defogger relay connector terminal No. 4 (Dark Blue/White wire). See Figure . If resistance is less than 5 ohms, replace BCM. If resistance is 5 ohms or more, repair open Dark Blue/White wire.
  10. Turn ignition off. Remove and inspect EBL (rear defogger) fuse from Power Distribution Center (PDC). PDC is located in engine compartment. See PDC cover label for fuse location. If fuse is open, go to next step. If fuse is not open, repair open Black/Pink wire between PDC and rear defogger relay.
  11. Using an external ohmmeter, measure resistance of Black/Pink wire between EBL fuse connector and rear defogger relay connector terminals No. 2 and 5. If resistance is less than 5 ohms on either circuit, repair Black/Pink wire for short to ground. Replace EBL fuse. If resistance is 5 ohms or more on both circuits, go to next step.
  12. Replace EBL fuse. Install rear defogger relay. Turn ignition on. Turn rear defogger on. If rear window defogger operates without blowing fuse, system is currently operating correctly. If rear window defogger operates and blows fuse, repair Black/Pink wire between EBL fuse and rear defogger relay for short to ground. Replace EBL fuse.
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