B2577

DTC B2577

CIRCUIT DESCRIPTION




The body control module (BCM) turns on the headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the headlamp relay at all times through the BACKUP/TURN fuse. The BCM grounds the headlamp relay control circuit in order to activate the relay.

CONDITIONS FOR RUNNING THE DTC
- The ignition switch is in the ON position.
- The ambient light sensor senses a light condition (automatic lamp control (ALC) headlamps off).

CONDITIONS FOR SETTING THE DTC
Either of the following conditions will set this DTC:
- The headlamp relay control circuit is open for 5 seconds.
- The headlamp relay control circuit is shorted to ground for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The SERVICE indicator will illuminate.

CONDITIONS FOR CLEARING THE DTC
- The conditions for setting the DTC are no longer present.
- A history DTC clears after 100 malfunction free ignition cycles.
- The BCM receives the clear code command from the scan tool.

DIAGNOSTIC AIDS
- If the headlamp relay control circuit is open, the ALC headlamps will be inoperative.
- In the headlamp relay control circuit is shorted to ground, the ALC headlamps will be always on.
- If the DTC is a history DTC, the problem may be intermittent.

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. Tests for voltage at the coil side of the headlamp relay. The BACKUP/TURN fuse supplies battery positive voltage to the coil side of the headlamp relay.
4. Verifies that the BCM is providing ground to the headlamp relay.
5. Tests if ground is constantly being applied to the headlamp relay.