Circuit Description
The Body Control Module (BCM) uses the ambient light sensor signal to control the automatic headlamp control system. The ambient light sensor is connected directly to the BCM through the DRL ambient light return and the DRL ambient light signal circuits.
Conditions for Running the DTC
The DRL feature of the automatic headlamp control feature must be enabled.
Conditions for Setting the DTC
| • | The BCM detects that the ambient light signal circuit is greater than 4 volts or is open when it is trying to enable the automatic headlamp control feature. |
| • | The condition above must be present for more than 0.3 seconds. |
Action Taken When the DTC Sets
| • | The BCM stores DTC B2648 in memory |
| • | The SERVICE VEHICLE SOON telltale illuminates |
| • | Headlamps, park lamps, tail lamps and marker lamps illuminate to night intensity |
Conditions for Clearing the DTC
| • | The BCM no longer detects the fault in the ambient light sensor circuit. |
| • | A history DTC B2648 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
| • | If the DTC B2648 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | The following conditions may cause an intermittent malfunction to occur: |
| - | An intermittent open in ambient light signal circuit |
| - | The ambient light sensor is intermittently open internally |
| - | The BCM is intermittently open internally |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
-
Tests for the proper operation of the circuit in the high voltage range.
-
Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Lighting System Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the ambient light sensor input parameter is within the specified range? | 0.25 -2.5 Volts | Go to Diagnostic Aids | Go to Step 3 |
Does the scan tool indicate that the ambient light sensor input parameter is greater than the specified value? | 2.5 Volts | Go to Step 4 | Go to Step 5 | |
Does the scan tool indicate that the ambient light sensor input parameter is less than the specified value? | 0.25 Volts | Go to Step 8 | Go to Step 6 | |
5 | Test the signal circuit of the ambient light sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
6 | Test the signal circuit of the ambient light sensor for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 |
7 | Test the ground circuit of the ambient light sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
8 | 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 12 | Go to Step 10 |
9 | 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 12 | Go to Step 11 |
10 | Replace the ambient light sensor. Refer to Daytime Running Lamp (DRL) Ambient Light Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 |
Important: Perform the set up procedure for the body control module. Replace the BCM. Refer to Body Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
