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 Descriptor
DTC B2645 00
- Ambient Light Sensor Circuit Voltage Out Of Range
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 HVAC control module determines the ambient light conditions, DAY or NIGHT, based on the voltage from the ambient light sensor. The HVAC control module provides a low reference ground and 5-volt reference signal to the ambient light sensor. The ambient light sensor signal circuit is a direct input to the HVAC control module. The HVAC control module sends a message via GMLAN serial data to the instrument panel module (IPM) indicating the outside light conditions based on the signal from the ambient light sensor. The IPM determines 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 IPM will command the DRLs ON. During low light conditions the IPM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation. With the turn signal/multifunction switch in the OFF position, the DRLs which consists of the front turn signal lamps will either be turned ON or OFF after a 30-second delay, depending on whether daylight or low light conditions are sensed by the ambient light sensor.
Conditions for Running the DTC
* The HVAC control module must be powered.
* DTC B1327 Battery Voltage Low, must not be current.
Conditions for Setting the DTC
Ambient light sensor voltage is less than 0.2 volt or greater than 4.9 volts on 3 consecutive tests.
Actions Taken When the DTC Sets
* The ambient light sensor will default to NIGHT status.
* The HVAC control module commands the Service A/C System indicator ON via GMLAN serial data.
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 40 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 (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 sunload sensor assembly.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 20.0 ohms of resistance between the low reference circuit terminal C 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 HVAC control module.
3. Reconnect the sunload sensor assembly harness connector.
4. Ignition ON, verify the scan tool ambient light sensor parameter is greater than 0.2 volts.
• If less than the specified range, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the HVAC control module .
5. Verify the scan tool ambient light sensor parameter is less than 4.9 volts.
• 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 HVAC control module.
6. If all circuits test normal, replace the sunload sensor assembly.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Sun Load Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for HVAC control module replacement, setup, and programming