Test No. 16: Rear Window Defogger Does Not Operate

Check rear window defogger relay. See REAR WINDOW DEFOGGER RELAY under COMPONENT TESTS. If rear window defogger relay is okay, go to next step. If rear window defogger relay is defective, replace rear window defogger relay and recheck rear window defogger operation.
Check wiring harness and electrical connectors between battery and rear window defogger relay, and between rear window defogger relay and body Electronic Control Unit (ECU). See WIRING DIAGRAMS in REAR WINDOW & MIRROR DEFOGGERS article. For additional wiring for power supply, see POWER DISTRIBUTION article in WIRING DIAGRAMS. Body ECU is located on instrument panel junction block and contains 12-pin, 22-pin and 25 pin electrical connectors. See Figure. If necessary to check DEF fuse (30-amp) and DEF RLY fuse (5-amp), these fuses are located in instrument panel junction block. See Figure. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector are defective, repair as necessary and recheck rear window defogger operation.
Check rear window defogger switch. See REAR WINDOW DEFOGGER SWITCH under COMPONENT TESTS. If rear window defogger switch is okay, go to next step. If rear window defogger switch is defective, replace rear window defogger switch and recheck rear window defogger operation.
Check body ECU for proper voltage and input signals. See BODY ELECTRONIC CONTROL UNIT under PIN VOLTAGE TESTS. If proper voltage and input signals exist, go to next step. If proper voltage and input signals do not exist, repair as necessary and recheck rear window defogger operation.
Replace body ECU with a known-good body ECU and recheck rear window defogger operation. If rear window defogger operates properly, original body ECU was defective. If rear window defogger still does not operate properly, check wiring harness and electrical connectors for body ECU, rear window defogger relay and rear window defogger switch for intermittent problem. See WIRING DIAGRAMS in REAR WINDOW & MIRROR DEFOGGERS article. Repair wiring harness or electrical connector as necessary.