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 02: Ambient Light Sensor Circuit Short to Ground

DTC B2645 05: Ambient Light Sensor Circuit Short to Battery or Open

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Ambient Light Sensor Signal

B2645 02

B2645 05

B2645 05

--

Headlamp - Left Front Low Beam Control

1

1

1

--

Headlamp - Right Front Low Beam Control

1

1

1

--

Ambient Light Sensor Low Reference

--

B2645 05

B2645 05

--

Headlamp - Left Front Ground

--

1

--

--

Headlamp - Right Front Ground

--

1

--

--

1. Headlamps Malfunction

2. Daytime Running Lamps Malfunction

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-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. 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 volts.

Conditions for Setting the DTC

B2645 02

The DTC will set when the BCM detects a short to ground in the ambient light sensor signal circuit.

B2645 05

The DTC will set when 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

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 for scan tool information

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
  2. Ignition OFF, exterior lamps OFF, key removed, wait 30 seconds, test for less than 10 ohms between the appropriate low reference circuit terminal listed below and ground.
  3. • Ambient light sensor low reference circuit terminal B - with C60
    • Ambient light sensor low reference circuit terminal C - with C68
    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.
  4. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 volts.
  5. If less than the specified range, test the appropriate signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the BCM.
    • Ambient light sensor signal circuit terminal A - with C60
    • Ambient light sensor signal circuit terminal D - with C68
  6. Install a 3 A fused jumper wire between the appropriate signal and low reference circuit terminals listed below. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 volts.
  7. • Ambient light sensor signal circuit terminal A and low reference circuit terminal B - with C60
    • Ambient light sensor signal circuit terminal D and low reference circuit terminal C - with C68
    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 BCM.
  8. If all circuits test normal, replace the ambient light sensor.

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