For 1990-2009 cars

### Circuit Description

The body control module (BCM) monitors the ambient light sensor signal circuit in order to determine if the daytime running lights (DRL) or the auto headlights (ALC) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor voltage is between 1.75-4.9 volts, either the DRL will be commanded ON or the ALC will be commanded ON.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2645 Ambient Light Sensor Circuit

### Conditions for Running the DTC

The system voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B2645 01

Will set if there is a short to voltage in the ambient light sensor signal circuit.

#### B2645 02

Will set if there is an open or short to ground in the ambient light sensor signal circuit.

### Action Taken When the DTC Sets

The ALC will remain ON in any ambient light state.

### Conditions for Clearing the MIL/DTC

• | This DTC will clear immediately after the condition for setting the fault is corrected.

• | A history DTC will clear after 100 consecutive ignition cycles without a fault present.

• | Use a scan tool in order to clear history and current DTCs.

### Diagnostic Aids

• | The following may cause an intermittent:

- | Bent terminal

- | Backed out terminal

- | Damaged terminal

- | Poor terminal tension

- | Chafed wire

- | Broken wire inside the insulation

• | When diagnosing for an intermittent short or an open, manipulate the wire harness while watching the test equipment for changes.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the Ambient Light Sensor parameter in the body control module (BCM) data list .

Does the scan tool indicate that the Ambient Light Sensor parameter is within the specified range?

1.75-4.9 V

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the ambient light sensor.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the Ambient Light Sensor parameter.

Does the scan tool indicate that the Ambient Light Sensor parameter is less than the specified value?

0.02 V

Go to Step 4

Go to Step 5

4 | Test the ambient light sensor circuit of the ambient light sensor for the following:

• | An open

• | A high resistance

• | A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 10

Go to Step 6

5 | Test the ambient light sensor signal circuit of the ambient light sensor for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7
6 | Inspect for poor connections at the harness connector of the ambient light sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8
7 | Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9
8 | Replace the ambient light sensor. Refer to Ambient Light Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
9 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | --
10 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK