B2648

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 circuit and a signal circuit to the ambient light sensor. The BCM will detect high voltage on the ambient light sensor signal circuit when ambient light is high, and low voltage when ambient light is low. The BCM monitors the ambient light sensor voltage at the signal circuit 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 82648 in the BCM memory.
^ The automatic headlamps and park lamps will remain ON.

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.
^ The BCM receives the Clear Code command from the scan tool.

DIAGNOSTIC AIDS
^ The following conditions may cause an intermittent malfunction:
- An intermittent short to voltage in the ambient light sensor signal circuit.
- An intermittent short to voltage in the ambient light sensor reference circuit.
^ If the ambient light sensor circuit is open or shorted (to ground or voltage), the BCM will command the automatic headlamps and park lamps 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 Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-3:

Steps 4-14:

The number(s) below refer to the step number(s) on the diagnostic table.
2. Tests ambient light sensor data using a scan tool.
3. Tests the ambient light sensor data with the sensor disconnected. The scan tool will display ambient light sensor voltage as 0 volts with the sensor disconnected.
4. Tests the ambient light sensor data with a jumper wire between the reference and signal circuit. The scan tool will display ambient light sensor voltage between 3.5-4.5 volts with the sensor jumpered.
5. Tests for a short to voltage in the 5 volt reference circuit.