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DTC B2645

DTC B2645

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptors

DTC B2645 03

Ambient Light Sensor Circuit Low Voltage

DTC B2645 07

Ambient Light Sensor Circuit High Voltage

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Ambient Light Sensor Signal B2645 03 B2645 03 B2645 07 -
Low Reference - B0163 05, B0183 05, B1405 05, B2645 07 - -


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 1.4-4.5 V depending on outside lighting conditions. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights or automatic lamp control when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the daytime running lights ON. During low light conditions the BCM will command the low beam headlamps ON.

Conditions for Running the DTC

Ignition ON

Conditions for Setting the DTC

B2645 03

The BCM detects a short to ground on the ambient light sensor signal circuit.

B2645 07

The BCM detects greater than 5 volts on the ambient light sensor signal circuit.

Action Taken When the DTC Sets

The automatic headlamps will malfunction.

Conditions for Clearing the DTC


• The DTC will be current for as long as the fault is present.

• When the fault is no longer present, the DTC will be a history DTC.

• A history DTC will clear after 50 ignition cycles.


Reference Information

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References

Circuit/System Verification

Ignition ON, observe the scan tool Ambient Light Sensor parameter. The reading should be between 1.4-4.5 V and change with ambient light changes.

Circuit/System Testing


1. Ignition OFF, disconnect the harness connector at the B10B Ambient Light/Sunload Sensor.

2. Test for less than 30 Ω between the low reference circuit terminal 6 and ground.

3. 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 K33 HVAC Control Module.

4. Ignition ON, test for 4.8-5.2 V between the signal circuit terminal 5 and ground.

5. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.

6. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

7. If all circuits test normal, replace the B10B Ambient Light/Sunload Sensor.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Sun Load Temperature and Daytime Running Lamp Ambient Light Sensor Replacement

• Control Module References for BCM or HVAC control module replacement, setup and programming