Circuit Description
The ambient light sensor circuit provides an input to the BCM for DRL and automatic headlight functions. This input allows the BCM to activate or deactivate DRL and automatic headlamps with different ambient light levels. The BCM supplies a 5 volt reference and a ground to the ambient light sensor. The BCM will detect high voltage on the ambient light sensor ground circuit when ambient light is high, and low voltage when ambient light is low. The BCM monitors the ambient light sensor voltage and determines if the voltage is within range. If the voltage is not within range, a malfunction is present and a DTC will set.
Conditions for Setting the DTC
| • | A short to voltage in the ambient light sensor circuit. |
| • | Condition must be present for 2 seconds. |
Action Taken When the DTC Sets
| • | Stores a DTC B2648 in the BCM memory. |
| • | The automatic headlamps and parklamps will remain ON. |
| • | No driver warning message will be displayed for this DTC. |
Conditions for Clearing the DTC
| • | The BCM no longer detects a short to voltage in the ambient light sensor circuit. |
| • | A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present. |
| • | Use the IPC clearing DTCs feature. |
| • | Use a scan tool. |
Diagnostic Aids
| • | The following conditions may cause an intermittent malfunction: |
| - | An intermittent short to voltage in CKT 1137. |
| - | An intermittent short to voltage in CKT 1138. |
| • | If the ambient light sensor circuit is open or shorted (to ground or voltage), the BCM will command the automatic headlamps and parklamps ON. If the ignition is cycled the BCM will retest for any malfunctions in the ambient light sensor circuit and if a malfunction is current the BCM will activate the automatic . |
| • | If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Refer to Intermittents and Poor Connections Diagnosis . |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
This test checks the ambient light sensor data using a scan tool. The scan tool will display ambient light sensor voltage over 4.0 volts if there is a short to voltage in the ambient light sensor circuit.
-
This test checks the ambient light sensor 5 volt reference and ground circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Were you sent here from the BCM Diagnostic System Check? | -- | ||
Does the scan tool display ambient light sensor data within the specified value? | 0.1-3.9 V | |||
Is the voltage indicated within the specified value? | 4.5-5.5 V | |||
4 | Check for a short to voltage in CKT 1137 and CKT 1138. Was a problem found and repaired? | -- | ||
5 | Replace the ambient light sensor. Refer to Daytime Running Lamp (DRL) Ambient Light Sensor Replacement in Lighting Systems. Is the replacement complete? | -- | -- | |
6 | Check the ambient light sensor circuit for an intermittent malfunction. Refer to Diagnostic Aids. Was a problem found and repaired? | -- | ||
7 |
Does DTC B2648 set as current? | -- | System OK | |
8 |
Is the replacement complete? | -- | -- | |
9 |
Is the repair complete? | -- | -- |
