GM Service Manual Online
For 1990-2009 cars only

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 Below Threshold

DTC B2645 07: Ambient Light Sensor Circuit Above Threshold

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Ambient Light Sensor Signal Circuit

B2645 07

B2645 03

B2645 07

B2645 03, 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 depending on outside lighting conditions. The body control module (BCM) provides a 10-volt 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. 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

    • DTC B2645 03 will set when the BCM detects voltage is low in the ambient light sensor signal circuit.
    • DTC B2645 07 will set when the BCM detects voltage is above 10 volts in the ambient light sensor signal circuit.

Action Taken When the DTC Sets

When DTC B2645 03 or B2645 07 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

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Testing

  1. Turn OFF the ignition.
  2. Disconnect the ambient light sensor.
  3. Turn ON the ignition.
  4. Install a scan tool and display the Ambient Light Sensor parameter in the BCM data list.
  5. If the scan tool parameter is less than 7 volts, locate and repair an open, high resistance, or short to ground in the ambient light sensor signal circuit, or replace the ambient light sensor.
    If the scan tool parameter is greater than 10.5 volts, locate and repair a short to voltage in the ambient light sensor signal circuit.
  6. If circuits test OK, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ambient Light Sensor Replacement
    •  Control Module References for BCM replacement, setup, and programming