For 1990-2009 cars

### Circuit Description

The ambient light sensor indicates the light level to control the automatic headlamps and park lamps. The body control module (BCM) provides a 5 volt reference signal to the light sensor through the ambient light sensor signal circuit. The BCM receives the modified voltage from the ambient light sensor through the ambient light sensor low reference circuit. A low voltage under 1.5V, signals a dark condition to the BCM and vice versa.

### Conditions for Running the DTC

The ignition switch is in the ON position.

### Conditions for Setting the DTC

Any of the following conditions will set this DTC:

• | The ambient light sensor signal reference circuit is open for 5 seconds.

• | The ambient light sensor signal reference circuit is shorted to ground for 5 seconds.

• | The ambient light sensor signal return circuit is open for 5 seconds.

• | The ambient light sensor signal return circuit is shorted to ground for 5 seconds.

### Action Taken When the DTC Sets

The headlamps and park lamps are always illuminated with the ignition ON.

### Conditions for Clearing the DTC

• | The conditions for setting the DTC are no longer present.

• | A history DTC clears after 100 malfunction free ignition cycles.

• | The BCM receives the clear code command from the scan tool.

### Diagnostic Aids

If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The normal operating voltage of the ambient light sensor (photocell) is 0.5-4.5 volts.

2. This step determines if there is a problem with the signal circuit of the ambient light sensor.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics
1 | Did you perform the Lighting System Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Lighting Systems
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the PHOTOCELL VOLTAGE data parameter in the LAMP STATUS data list.

Does the scan tool indicate that the PHOTOCELL VOLTAGE parameter is within the specified range?

0.5-4.5 volts

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

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. Probe the signal circuit of the ambient light sensor with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 5

4 |

1. Connect a fused jumper wire between the signal circuit of the ambient light sensor and the low reference circuit of the ambient light sensor.
2. With a scan tool, observe the PHOTOCELL VOLTAGE data parameter in the LAMP STATUS data list.

Does the scan tool indicate that the PHOTOCELL VOLTAGE parameter is within the specified range?

4.5-5.0 volts

Go to Step 7

Go to Step 6

5 | Test the signal circuit of the ambient light sensor for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
6 | Test the low reference circuit of the ambient light sensor for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
7 | 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 in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
8 | Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
9 | Replace the ambient light sensor. Did you complete the replacement? | -- | Go to Step 11 | --
10 | Important: Perform the set up procedure for the body control module. Replace the body control module. Refer to Body Control Module Replacement in Body Control System. Did you complete the replacement? | -- | Go to Step 11 | --
11 |

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