B2578

DTC B2578

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 dark condition (automatic lamp control (ALC) headlamps on).

CONDITIONS FOR SETTING THE DTC
The headlamp relay control circuit is shorted to voltage for 1 second.

ACTION TAKEN WHEN THE DTC SETS
- The BCM turns off the headlamp relay control for the remainder of the ignition cycle.
- The SERVICE indicator illuminates.

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 DTC is a history DTC, the problem may be intermittent.

TEST DESCRIPTION

Steps 1-6:

The number below refers to the step number 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.