2010 Cadillac CTS Sedan AWD V6-3.6L Page 518
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 V depending on outside lighting conditions. The HVAC control module provides a low reference ground and 5 V reference signals to
the ambient light sensor. 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 (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 03
The BCM detects a short to ground in the ambient light sensor signal circuit.
B2645 07
The BCM detects a short to voltage or an open/high resistance 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 (See: Diagrams/Electrical Diagrams/Lighting and Horns/System
Diagram/Headlights/Daytime Running Lights (DRL) Schematics)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (See: Lighting and Horns/Description and Operation/Exterior Lighting Systems Description
and Operation)
Electrical Information Reference
* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/Circuit Testing/Circuit Testing)
* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/Connector Repairs/Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/Circuit
Testing/Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/Wiring Repairs/Wiring Repairs)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning)for scan tool information
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the ambient light/sunload sensor.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 10.0 ohm between the low reference circuit terminal C and ground.
瀚慖f 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. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 V.
瀚慖f less than the specified range, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the BCM.
