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Test No. 12: Automatic Light Control System Does Not Operate

  1. Check operation of automatic light control system and automatic light control sensor. See AUTOMATIC LIGHT CONTROL SYSTEM & AUTOMATIC LIGHT CONTROL SENSOR  under COMPONENT TESTS. If automatic light control system operates properly, go to next step. If automatic light control system does not operate properly, replace automatic light control sensor and recheck automatic light control system operation.
  2. Check wiring harness and electrical connectors between automatic light control sensor and body Electronic Control Unit (ECU) for an intermittent problem. 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 connector are okay, go to next step. If wiring harness or electrical are defective, repair as necessary and recheck automatic light control system operation.
  3. It may be possible that automatic light control sensor is defective or has an intermittent problem. Replace automatic light control sensor and recheck automatic light control system operation. If automatic light control system does not operate properly, go to next step. If automatic light control system operates properly, the original automatic light control sensor was defective.
  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 automatic light control system operation. See HEADLIGHT CONTROL SWITCH  under REMOVAL & INSTALLATION.
  5. Check wiring harness and electrical connectors between headlight control switch and body ECU. See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article and 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 automatic light control system 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 automatic light control system operation.
  7. Replace body ECU with a known-good body ECU and recheck automatic light control system operation. If automatic light control system operates properly, original body ECU was defective. If automatic light control system still does not operate properly, check wiring harness and electrical connectors for body ECU and automatic light control system for intermittent problem. See WIRING DIAGRAMS in DAYTIME RUNNING LIGHTS article. Repair wiring harness or electrical connector as necessary.
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