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

### Circuit Description

DTC B2647 (both current and history) indicates a short to ground or open 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 is shorted for 5 seconds.

### Action Taken When the DTC Sets

• | The headlamps are always on at full intensity.

• | Stores DTC B2647 in the body control module (BCM) memory.

### 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 DTC(s) 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 ground in CKT 1138 between the Body Control Module (BCM) and the ambient light sensor.

1. This step determines an open 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 to measure the resistance in CKT 1138 between the Ambient Light Sensor connector terminal B and ground.

Is the measured resistance equal to the specified value?

∞

Go to Step 4

Go to Step 3

3 | Repair the short to ground 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 7 | --
4 | Use the J 39200 DMM in order to measure the resistance in CKT 1138 between the Ambient Light Sensor connector terminal B and the BCM connector C2 terminal A3. Is the measured resistance within the specified range? | 0-2 ohms | Go to Step 9 | Go to Step 5
5 | Repair the open 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 Body Control Module System Check | --
6 | Replace the Ambient Light Sensor. Is the repair complete? | -- | Go to Step 7 | --
7 |

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

Did DTC B2647 clear from memory?

--

Go to Body Control Module System Check

Go to Step 8

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

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

• | BCM Replacement in Instrument Panel, Gauges and Console

Is the repair complete?

--

Go to Body Control Module System Check

--

9 | Use J 39200 DMM in order to measure the resistance between the Ambient Light Sensor connector terminal A and the BCM connector C2 terminal B2. Is the measured resistance within the specified range? | 0-2 ohms | Go to Step 11 | Go to Step 10
10 | Repair the open in CKT 1137. A3. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 7 | --
11 | Use J 39200 DMM in order to measure the resistance between the BCM connector C2 terminal B2 and ground. Is the measured resistance equal to the specified value? | ∞ | Go to Step 6 | Go to Step 12
12 | Repair the short to ground in CKT 1137. A3. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 7 | --