Circuit Description
The body control module (BCM) uses the daytime running lamps (DRL) ambient light sensor signal to control the automatic headlamp system. The DRL ambient light sensor is connected directly to the BCM through the DRL ambient light sensor signal circuit and the DRL ambient light low reference circuits.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2648 Ambient Light Sensor Circuit Low
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 that the DRL ambient light sensor signal circuit is greater than 4 volts or is open when it is trying to enable the automatic headlamp control feature. |
| • | The DRL ambient light sensor signal circuit is open or shorted to battery positive voltage. |
| • | The ambient light sensor is open internally. |
| • | 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 DRL ambient light sensor signal. |
| • | A history DTC B2648 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
Diagnostic Aids
| • | If the DTC B2648 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | The following conditions may cause an intermittent malfunction to occur: |
| - | An intermittent open in DRL ambient light sensor signal circuit |
| - | The DRL ambient light sensor is intermittently open internally. |
| - | The BCM is intermittently open internally. |
Step | Action | Values | 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 |
2 |
Does the scan tool indicate that the Ambient Light Sensor Input parameter is within the specified range? | 0.25 -2.5 V | Go to Diagnostic Aids | Go to Step 3 |
3 |
Does the scan tool indicate that the DRL Ambient Light Sensor Input parameter is greater than the specified value? | 4.9 V | Go to Step 4 | Go to Step 5 |
4 |
Does the scan tool indicate that the DRL Ambient Light Sensor Input parameter is less than the specified value? | 0.25 V | Go to Step 8 | Go to Step 6 |
5 | Test the DRL ambient light sensor signal circuit for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
6 | Test the DRL ambient light sensor signal circuit for a short to battery positive voltage, a high resistance, or an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 |
7 | Test the DRL ambient light sensor low reference circuit for a high resistance or an open. Refer to Circuit Testing and to 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 DRL ambient light sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to 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 BCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the DRL 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 BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
