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Test No. 13: 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.
  2. Check wiring harness and electrical connectors for Light Green/Red wire between headlight control switch and body Electronic Control Unit (ECU) for the taillights. See WIRING DIAGRAMS in EXTERIOR LIGHTS article. Body ECU is located at driver's side of instrument panel on the fuse/relay box and contains an 18-pin and 20-pin electrical connector. See Figure. 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.
  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 ECU. See WIRING DIAGRAMS in EXTERIOR LIGHTS article. 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 between body ECU and taillight relay, and wiring circuit for taillights for intermittent problem. See WIRING DIAGRAMS in EXTERIOR LIGHTS article. Repair wiring harness or electrical connector as necessary.
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