B2645
DTC B2645
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) 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 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground and 5 V 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.
Conditions for Running the DTC
Battery voltage must be between 9-16 V.
Conditions for Setting the DTC
B2645 02
The BCM detects a short to ground in the ambient light sensor signal circuit.
B2645 05
The BCM detects a short to voltage or an open in the ambient light sensor signal circuit.
Actions Taken When the DTC Sets
* Automatic lamp control (ALC) is inoperative.
* The BCM defaults to low light status and commands the low beam headlamps ON.
Conditions for Clearing the DTC
* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
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 (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
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 10 ohm between the low reference circuit terminal B and ground.
• 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 V.
• If less than the specified range, test the signal circuit terminal A for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
4. Install a 3 A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 V.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
5. 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