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Test No. 10: Headlights Do Not Operate

  1. Check bulbs for headlights. If bulbs are okay, go to next step. If bulbs are defective, replace bulbs and recheck headlight operation.
  2. 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 headlight operation. See HEADLIGHT CONTROL SWITCH  under REMOVAL & INSTALLATION.
  3. Check wiring harness and electrical connectors between headlight control switch and body Electronic Control Unit (ECU). See WIRING DIAGRAMS in DAYTIME RUNNING 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 headlight operation.
  4. Check headlight relay. See HEADLIGHT RELAY  under COMPONENT TESTS. Headlight relay may also be referred to as HEAD relay. If headlight relay is okay, go to next step. If headlight relay is defective, replace headlight relay and recheck headlight operation.
  5. Check wiring harness and electrical connectors between battery and headlight relay, and between headlight relay and body ECU. See WIRING DIAGRAMS in DAYTIME RUNNING 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 headlight 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 do not exist, repair as necessary and recheck headlight operation.
  7. Replace body ECU with a known-good body ECU and recheck headlight operation. If headlights operate properly, original body ECU was defective. If headlights still do not operate properly, check wiring harness and electrical connectors for body ECU and headlights for intermittent problem. See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article. Repair wiring harness or electrical connector as necessary.
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