B2575

DTC B2575

CIRCUIT DESCRIPTION
The body control module (BCM) monitors and supplies battery voltage to the headlamp relay on the headlamp relay coil supply voltage circuit. When the ambient light sensor is in the DARK state and the headlamp and panel dimmer switch is in the AUTO mode, the BCM supplies battery voltage to the headlamp relay to power up the headlamps. The BCM monitors the headlamp relay coil supply voltage circuit to determine when the daytime running lights (DRL) should be ON or OFF. When the BCM detects battery voltage on the headlamp relay coil supply voltage circuit it will turn OFF the DRL. When the BCM detects the headlamp relay coil supply voltage circuit is low it will turn ON the DRL when the DRL conditions are present.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC B2575 Headlamp Control Circuit

CONDITIONS FOR RUNNING THE DTC
- The battery voltage must be between 9-16 volts.
- Ignition switch in the RUN position.
- The headlamp and panel dimmer switch must be turned to the ON position or the ambient light sensor must be in the DARK state with the headlamp and panel dimmer switch in the AUTO position.
- The park brake must be released.

CONDITIONS FOR SETTING THE DTC
- The headlamps and panel dimmer switch in the AUTO mode.
- The ambient light sensor state is in the DARK state.
- The headlamp relay coil supply voltage circuit is shorted to ground.
- The above conditions must be met for 0.5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The headlamps will not operate with the headlamp and panel dimmer switch in the AUTO position and the ambient light state is DARK.

CONDITIONS FOR CLEARING THE MIL/DTC
- The DTC will clear immediately after the short to ground on the headlamp relay coil supply voltage circuit is repaired or the next fault free ignition cycle.
- A history DTC will clear after 100 consecutive ignition cycles without a fault present.
- History and current DTCs can be cleared using a scan tool.

DIAGNOSTIC AIDS
If the headlamps are manually turned ON when the headlamp relay coil supply voltage circuit is shorted to ground, the TBC fuse will open and the headlamp and panel dimmer switch can be damaged. When the TBC fuse opens, the scan tool will lose communication with the BCM.
- Perform a visual check for loose or poor connections at all related components.

TEST DESCRIPTION

Steps 1 - 13:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the headlamp relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Verifies that the body control module is providing voltage to the headlamp relay.
4. Tests for an open in the ground circuit to the headlamp relay.
5. Tests if voltage is constantly being applied to the headlamp relay.
6. Tests for a short to ground on the control circuit of the headlamp relay.
12. After replacement of the BCM you must calibrate the new module for proper operation.