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Test No. 11: All Taillights Do Not Operate

  1. Check TAIL fuse (10-amp). TAIL fuse is located in fuse/relay box at driver's side of instrument panel. See Figure. If fuse is okay, go to next step. If fuse is defective, repair short in wiring connected to this fuse. See WIRING DIAGRAMS in EXTERIOR LIGHTS article.
  2. 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.
  3. 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. Body ECU is located at driver's side of instrument panel on the fuse/relay box. See Figure. Electrical connector B4 (25-pin) and electrical connector B5 (25-pin) are located at each side of body ECU and a 12-pin electrical connector at rear of body ECU. 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.
  4. 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.
  5. Check wiring harness and electrical connectors between headlight control switch and body ECU for the taillights. See WIRING DIAGRAMS in HEADLIGHT SYSTEMS or DAYTIME RUNNING LIGHTS article. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary and recheck taillight operation.
  6. 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 does not exist, repair as necessary and recheck taillight operation.
  7. 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 system for an intermittent problem. See WIRING DIAGRAMS in EXTERIOR LIGHTS article. Repair wiring harness or electrical connector as necessary.
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