B2647

DTC B2647 Ambient Light Sensor Circuit Low:

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
^ An open in the ambient light sensor circuit.
^ A short to ground in CKT 1138.
^ Condition must be present for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ Stores a DTC B2647 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 an open or short to ground 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 PC clearing DTCs feature.
^ Use a scan tool.

DIAGNOSTIC AIDS
^ The following conditions may cause an intermittent malfunction:
- An intermittent short to ground in CKT 1138.
- An intermittent open in CKT 1137.
- The ambient light sensor is shorted or open internally.
^ 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. Testing and Inspection

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table:
2. This test checks the ambient light sensor data using a scan tool. The scan tool will display ambient light sensor voltage as 0 volts if there is an open or short to ground in the ambient light sensor circuit.
3. This test checks the ambient light sensor 5 volt reference and ground circuit.