The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground and 5-volt reference signal to the ambient light sensor. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the DRLs ON. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.

Battery voltage must be between 9-16 volts.

B2645 02

The DTC will set when the BCM detects a short to ground in the ambient light sensor signal circuit.

B2645 05

The DTC will set when the BCM detects a short to voltage or an open in the ambient light sensor signal circuit.

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, exterior lamps OFF, key removed, wait 30 seconds, test for less than 10 ohms between the appropriate low reference circuit terminal listed below and ground.

•	Ambient light sensor low reference circuit terminal B - with C60

•	Ambient light sensor low reference circuit terminal C - with C68

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

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 appropriate signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the BCM.

•	Ambient light sensor signal circuit terminal A - with C60

•	Ambient light sensor signal circuit terminal D - with C68

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

•	Ambient light sensor signal circuit terminal A and low reference circuit terminal B - with C60

•	Ambient light sensor signal circuit terminal D and low reference circuit terminal C - with C68

⇒	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, replace the ambient light sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.