The ambient light sensor is used to monitor outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. The sensor is a variable resistor, it's resistance changes as outside lighting conditions changes. With the headlamp switch in the AUTO position, the BCM monitors the sensor signal circuit to determine if the outside lighting conditions are correct for either daytime running lamps (DRL) or headlamp low beam operation. In daylight conditions, the BCM will command the DRLs ON. In low light conditions, the BCM will command the low beam headlamps ON.

The BCM defaults to low light status and commands the low beam headlamps ON.

A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, verify that a test lamp illuminates between the low reference circuit terminal B and ground.

⇒	If the test lamp does not illuminate, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify that a test lamp illuminates between the signal circuit terminal A and ground.

⇒	If the test lamp does not illuminate, test the signal circuit for an short to ground open/high resistance. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, test or replace the ambient light sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.