B2645

DTC B2645

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.



DTC Descriptors
DTC B2645 02
- Ambient Light Sensor Circuit Short to Ground

DTC B2645 05
- Ambient Light Sensor Circuit Short to Battery or Open




Diagnostic Fault Information






Circuit/System Description

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 2-4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground and a 5-volt reference signal to the ambient light sensor. The BCM monitors the daytime running lamps (DRL) ambient light sensor signal circuit to determine if outside lighting conditions are correct for either DRL or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In high outside light conditions the BCM will command the DRLs ON. In low light conditions, when the headlamps switch is in AUTO position, the BCM will command the low beam headlamps ON.


Conditions for Running the DTC

Battery voltage must be between 9-16 volts.


Conditions for Setting the DTC

B2645 02

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

B2645 05

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


Action Taken When the DTC Sets

When DTC B2645 02 or B2645 05 is present, the ALC will default to ON.


Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* You issue a scan tool CLEAR DTCs command.
* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Diagram 1)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 20 ohms of resistance between the low reference circuit terminal B and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify the scan tool ambient light sensor parameter is between 1-5 volts.

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


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

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



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Ambient Light Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for BCM replacement, setup, and programming