Circuit Description
The Body Control Module (BCM) uses the headlamp auto control ambient light sensor signal to control the automatic headlamp control system. The headlamp auto control ambient light sensor is connected directly to the BCM through the headlamp auto control ambient light signal circuit and the headlamp auto control ambient light ground reference circuit.
Conditions for Running the DTC
The DRL feature or the automatic headlamp control feature must be enabled.
Conditions for Setting the DTC
| • | The BCM detects a short to ground in the headlamp auto control ambient light ground reference circuit. |
| • | The condition above must be present for more than 0.3 seconds. |
Action Taken When the DTC Sets
| • | The BCM stores DTC B2647 in memory. |
| • | The SERVICE VEHICLE SOON telltale will illuminate |
| • | The headlamps, park lamps, tail lamps and marker lamps will illuminate to night intensity. |
Conditions for Clearing the DTC
| • | The BCM no longer detects a short to ground in the headlamp auto control ambient light sensor signal circuit. |
| • | A history DTC B2647 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
Diagnostic Aids
| • | If the DTC B2647 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 short to ground in the headlamp auto control ambient light signal circuit |
| - | The ambient light sensor is intermittently shorted to ground internally |
| - | The BCM is intermittently shorted to ground 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 | Go toA Diagnostic System Check - Lighting Systems in Lighting Systems. |
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 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 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 headlamp auto control ambient light sensor. Refer to Daytime Running Lamp (DRL) Ambient Light Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the Body Control Module. Refer to Body Control Module Replacement in Body Control Systems. Important: Perform the set up procedure for the Body Control Module. Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
