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Test No. 11: Taillights Do Not Operate

  1. Check headlight control switch. See HEADLIGHT CONTROL SWITCH  under COMPONENT TESTS. If headlight control switch is okay, go to next step. If headlight control switch is defective, replace headlight control switch and recheck taillight operation. See HEADLIGHT CONTROL SWITCH  under REMOVAL & INSTALLATION.
  2. Check wiring harness and electrical connectors between headlight control switch and body Electronic Control Unit (ECU). See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article and see WIRING DIAGRAMS in EXTERIOR LIGHTS article. Body ECU is located on instrument panel junction block and contains 12-pin, 22-pin and 25 pin electrical connectors. 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 taillight operation.
  3. Check taillight relay. See TAILLIGHT RELAY  under COMPONENT TESTS. If taillight relay is okay, go to next step. If taillight relay is defective, replace taillight relay and recheck taillight operation.
  4. Check wiring harness and electrical connectors between battery and taillight relay, and between taillight relay and body Electronic Control Unit (ECU). See WIRING DIAGRAMS in EXTERIOR LIGHTS article. For additional wiring for power supply, see GROUND 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 ALT fuse (120-amp), this fuse in located in fuse/relay box at driver's side front corner of engine compartment. See Figure. If necessary to check TAIL fuse (10-amp), this fuse is 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 taillight operation.
  5. 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 taillight operation.
  6. Replace body ECU with a known-good body ECU and recheck taillight operation. If taillights operate properly, original body ECU was defective. If taillights still do not operate properly, check wiring harness and electrical connectors for body ECU and taillight for intermittent problem. See WIRING DIAGRAMS in EXTERIOR LIGHTS article. Repair wiring harness or electrical connector as necessary.
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