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Test No. 12: Headlights 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 headlight operation.
  2. Check wiring harness and electrical connectors for Red wire between headlight control switch and body Electronic Control Unit (ECU) for the headlights. See WIRING DIAGRAMS in HEADLIGHT SYSTEMS article or DAYTIME RUNNING 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 headlight operation.
  3. Check headlight relay. See HEADLIGHT RELAY  under COMPONENT TESTS. If headlight relay is okay, go to next step. If headlight relay is defective, replace headlight relay and recheck headlight operation.
  4. Check wiring harness and electrical connectors between battery and headlight relay, and between headlight relay and body ECU. See WIRING DIAGRAMS in HEADLIGHT SYSTEMS article or DAYTIME RUNNING LIGHTS article. On models with daytime running lights, it may be necessary to check daytime running light relay, DRL relay and headlight dimmer relay. For relay testing, see DAYTIME RUNNING LIGHT RELAY , DRL RELAY  and HEADLIGHT DIMMER RELAY  under COMPONENT TESTS. If wiring harness and electrical connector are okay, go to next step. If wiring harness or electrical are defective, repair as necessary and recheck headlight 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 headlight operation.
  6. 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 between body ECU and headlights for intermittent problem. See WIRING DIAGRAMS in HEADLIGHT SYSTEMS article or DAYTIME RUNNING LIGHTS article. Repair wiring harness or electrical connector as necessary.
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