B2578

DTC B2578 Headlamp Relay Output Short To Battery:

CIRCUIT DESCRIPTION
This is a trouble code (both current and history) that indicates that the ALC headlamp relay control output is shorted to the battery.

CONDITIONS FOR SETTING THE DTC
Meet all of the following conditions:
^ The ambient light sensor indicates bright conditions.
^ The ALC option is enabled.
^ The ACL headlamp output is active.
^ The ALC headlamp feedback is present for one second.

ACTION TAKEN WHEN THE DTC SETS
^ Turns off the ALC headlamp relay.
^ Enters the fault state.
^ Stores the DTC B2578 in the BCM memory.
^ The SERVICE VEHICLE SOON indicator will illuminate.

CONDITIONS FOR CLEARING THE DTC
^ The fault state is exited upon program return to the ALC headlamp OFF state.
^ All the BCM history codes will be cleared after 100 ignition cycles (from OFF to RUN) with no current codes active during the 100 ignition cycles.
^ Use the scan tool.

DIAGNOSTIC AIDS
If the DTC is a history DTC, the problem may be intermittent. Try performing the above tests while wiggling the wiring and connectors. This can often cause the malfunction to appear.

TEST DESCRIPTION
The numbers below refer to the numbers on the diagnostic table.
2. This step verifies proper operation of the ALC headlamp relay.
3. This step determines if a short to battery exists in CKT 1970 within the underhood wiring harness junction block.
5. This step determines if a short to battery exists in CKT 1970 between the underhood wiring harness junction block and the body control module (BCM).