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 ambient light sensor through the ambient light sensor signal reference circuit. The BCM receives the modified voltage from the ambient light sensor through the ambient light sensor signal return circuit. A low voltage, under 1.5 volts, signals a dark condition to the BCM and vice versa.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2648 Ambient Light Sensor Circuit High
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 shorted to battery for 5 seconds. |
| • | The ambient light sensor signal reference circuit is shorted to battery for 5 seconds. |
Action Taken When the DTC Sets
| • | The ALC headlamp and park lamp relay control are disabled for the remainder of the ignition cycle. |
| • | The SERVICE indicator illuminates. |
| • | The check gages chime sounds. |
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.
-
The normal operating voltage of the photocell is 0.5-4.5 volts.
-
If the value is above 0.5 volts, with the sensor disconnected, a short to voltage exists. If the value is below 0.5 volts, a short to ground exists.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Does the scan tool indicate that the PHOTOCELL VOLTAGE parameter is within the specified range? | 0.5-4.5 V | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 | |
Does the scan tool indicate that the PHOTOCELL VOLTAGE data parameter is greater than the specified value? | 0.5 V | Go to Step 5 | Go to Step 4 | |
4 | Test the signal circuit and the ground circuit of the ambient light sensor for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 6 |
5 | Test the signal circuit and the ground circuit of the ambient light sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 in Wiring Systems. 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 body control module (BCM). 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 10 | Go to Step 9 |
8 | Replace the ambient light sensor. Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
