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.

B2645 03

The DTC will set when the BCM detects the ambient light sensor signal voltage is below 0.196 volts.

B2645 07

The DTC will set when the BCM detects the ambient light sensor signal voltage is above 4.9 volts.

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

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, test for less than 5 ohms between the appropriate ground circuit listed below and ground.

•	Terminal B (with C67)

•	Terminal C (with CJ2)

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 volts.

⇒	If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the appropriate signal circuit and the ground listed below. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 volts.

•	Terminal A and terminal B (with C67)

•	Terminal D and terminal C (with CJ2)

⇒	If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.