B2648

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematics:

CIRCUIT DESCRIPTION
The Body Control Module (BCM) monitors CKT 278 in order to determine if the Daytime Running Lights (DRL) or the Auto Headlights (AHL) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor voltage between 1.7-4.7 volts (light state) the DRL will be commanded ON. When the BCM senses the ambient light sensor voltage between 0.2-1.0 volts (dark state) the AHL will be commanded ON.

CONDITIONS FOR RUNNING THE DTC
- The system voltage must be between 9.0 and 16.0 volts.
- The ignition switch must be in the RUN position.
- The park brake must be released.
- The headlamp switch must be in the AUTO position.

CONDITIONS FOR SETTING THE DTC
- When the ambient light sensor input voltage is greater than 4.78 volts (CKT 278 is shorted to the battery).
- The above conditions must be met for 0.5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The AHL will remain ON in any ambient light state.

CONDITIONS FOR CLEARING THE MIL/DTC
- This DTC will clear immediately after the condition for setting the fault is corrected.
- A history DTC will clear after 100 consecutive ignition cycles without a fault present.
- Use a scan tool in order to immediately clear history and current DTCs.

DIAGNOSTIC AIDS
- Perform a visual inspection for loose or poor connections at all related components.
- Refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
3. Tests for the proper operation of the circuit in the low voltage range.
4. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
5. Tests for a short to voltage in the 5 volt reference circuit.
13. After replacement of the BCM you must calibrate the new module for proper operation.