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Test No. 8: Taillight Does Not Operate

  1. 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.
  2. 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 may also be referred to as integration relay. Electrical connector I13 (7-pin or 25-pin) and electrical connector I16 (18-pin) are located at body ECU and a 12-pin electrical connector is located at rear of body ECU. See Figure. If wiring harness and electrical connector are okay, go to next step. If wiring harness or electrical are defective, repair as necessary and recheck taillight operation.
  3. 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.
  4. Check wiring harness and electrical connectors between headlight control switch and body ECU. See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article. If wiring harness and electrical connector are okay, go to next step. If wiring harness or electrical 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 taillight operates properly, original body ECU was defective. If taillight still does not operate properly, check wiring harness and electrical connectors for body ECU for an intermittent problem. See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article. Repair wiring harness or electrical connector as necessary.
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