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Auto Headlights And/Or Fog Lights Not Operating Properly

NOTE: Perform EXTERIOR LIGHT TEST 1A  before proceeding with this test. For connector terminal identification and wiring diagrams, see BODY CONTROL COMPUTER - INTRODUCTION. Perform VERIFICATION TEST: VER-2A  after each repair.
CAUTION: Always turn ignition switch to OFF position prior to disconnecting or connecting any module connector.
    NOTE: Following test assumes that headlight and fog light systems are functioning correctly in manual mode.
  1. Ensure headlight switch is in auto headlight IN position. Using scan tool, select BODY COMPUTER, then SENSORS. Read HEADLAMP SWITCH VOLTAGE. If voltage is about 2.3 volts, go to next step. If voltage is not about 2.3 volts, replace headlight switch.
  2. Pull headlight switch knob out to fog light auto mode. Read HEADLAMP SWITCH VOLTAGE. If voltage is about 3.7 volts, go to next step. If voltage is not about 3.7 volts, replace
  3. Shine light on sun sensor. Using scan tool, read AUTO HEADLAMP SENSOR volts. If AUTO HEADLAMP SENSOR voltage is about zero volts, go to next step. If AUTO HEADLAMP SENSOR voltage is not about zero volts, go to step  5.
  4. Cover up sun sensor. Read AUTO HEADLAMP SENSOR volts. If AUTO HEADLAMP SENSOR voltage is about 5 volts, replace Body Control Module (BCM). BCM is mounted to junction block located behind left end cap of instrument panel. See Figure. If AUTO HEADLAMP SENSOR voltage is not about 5 volts, go to step  5.
  5. Disconnect sun sensor 4-pin connector. Read AUTO HEADLAMP SENSOR volts. If AUTO HEADLAMP SENSOR voltage is about 5 volts, go to next step. If AUTO HEADLAMP SENSOR voltage is not about 5 volts, go to step  8.
  6. Connect jumper wire between terminals No. 3 and 4 on sun sensor harness connector. Read AUTO HEADLAMP SENSOR volts. If AUTO HEADLAMP SENSOR voltage is about zero volts, replace sun sensor. If AUTO HEADLAMP SENSOR voltage is not about zero volts, remove jumper wire and go to next step.
  7. Connect jumper wire between ground and terminal No. 4 on sun sensor harness connector. Read AUTO HEADLAMP SENSOR volts. If AUTO HEADLAMP SENSOR voltage is about zero volts, repair open ground circuit. If AUTO HEADLAMP SENSOR voltage is not about zero volts, repair open sun sensor signal circuit.
  8. Disconnect Body Control Module (BCM) 24-pin Black connector C2. BCM is mounted to junction block located behind left end cap of instrument panel. See Figure. Using ohmmeter, measure resistance between ground and terminal No. 4 (Dark Blue wire) on sun sensor harness connector. If resistance is 5 ohms or greater, replace Body Control Module (BCM). BCM is mounted to junction block located behind left end cap of instrument panel. See Figure. If resistance is less than 5 ohms, repair Dark Blue wire for short to ground.
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