For 1990-2009 cars
Body Control Module Components
Body Control System Schematics

### Circuit Description

DTC B2648 (both current and history) indicates a short to battery in the ambient light sensor signal circuit.

### Conditions for Setting the DTC

All of the following conditions must be met:

• | The Automatic Lighting Control (ALC) option is enabled.

• | Ignition 1 is active.

• | The ambient light sensor analog input is shorted to B+ for 5 seconds.

### Action Taken When the DTC Sets

• | Stores DTC B2648 in the body control module (BCM) memory.

• | The SERVICE VEHICLE SOON indicator illuminate.

• | The check gauges chime sounds.

### Conditions for Clearing the DTC

• | The BCM goes to sleep and reinitializes with the fault cleared.

• | All BCM history codes clear after 100 ignition cycles (from OFF to ON) with no current codes active.

• | Clear history and current DTCs using a Scan Tool scan tool.

### Diagnostic Aids

If the DTC is a history DTC the problem may be intermittent. Perform the above tests while wiggling the wiring and connectors. This may often cause the malfunction to appear.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. This step determines a short to battery in CKT 1138 between the Body Control Module (BCM) and the Ambient Light Sensor.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Important: A short to ground will cause an open fuse(s). Before performing this diagnostic procedure, inspect the fuse(s) for an open.
1 | Was the Body Control Module (BCM) System Check performed? | -- | Go to Step 2 | Go to Body Control Module System Check
2 |

1. Disconnect the Ambient Light Sensor.
2. Disconnect the BCM connector C2.
3. Use the J 39200 DMM in order to measure the voltage in CKT 1138 between the Ambient Light Sensor connector terminal B and ground.

Is the measured resistance equal to the specified value?

0V

Go to Step 4

Go to Step 3

3 | Repair the short to B+ in CKT 1138 between the Ambient Light Sensor connector terminal B and the BCM connector C2 terminal A3. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 5 | --
4 | Replace the ambient light sensor. Is the repair complete? | -- | Go to Step 5 | --
5 |

1. Reconnect all disconnected components.
2. Clear the DTCs from memory.

Did DTC B2648 clear from memory?

--

Go to Step 7

Go to Step 6

6 | Replace the BCM. Refer to the following procedures:

• | Body Control Module (BCM) Programming/RPO Configuration

• | Body Control Module (BCM) Replacement

Is the repair complete?

--

Go to Step 7

--

7 | Clear the DTCs from memory. Are the DTCs cleared from memory? | -- | Go to Body Control Module System Check | --