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 Voltage Below Threshold

DTC B2645 07: Ambient Light Sensor Circuit Voltage Above Threshold

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Ambient Light Sensor Signal

B2645 03

B2645 07

B2645 07

--

Left Sun Load Sensor Signal

B0183 06

B0183 06

B0183 06

--

Right Sun Load Sensor Signal

B0188 06

B0188 06

B0188 06

--

Left Front Turn Signal Lamp Control

1

1

1

--

Right Front Turn Signal Lamp Control

1

1

1

--

Ambient Light Sensor Low Reference

--

B2645 07

B0183 06, B0188 06

--

Turn Signal Lamp - LF Ground

--

1

1

--

Turn Signal Lamp - RF Ground

--

1

1

--

1. Turn Signal Lamps and/or Indicators 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 HVAC control module provides a low reference ground and 5-volt 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. 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

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

B2645 03

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

B2645 07

The DTC will set when 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

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 sunload/ambient light sensor.
  2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 20.0 ohms between the low reference circuit terminal C and ground.
  3. 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.
  4. Reconnect the sunload sensor assembly harness connector.
  5. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 0.2 volts.
  6. If less than the specified range, test the signal circuit terminal D for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. Verify the scan tool Ambient Light Sensor parameter is less than 4.9 volts.
  8. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  9. If all circuits test normal, replace the sunload/ambient light sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ambient Light Sensor Replacement
    •  Control Module References for BCM or HVAC control module replacement, setup, and programming