B2578

CIRCUIT DESCRIPTION
The Body Control Module (BCM) controls the headlamp relay. The BCM grounds the headlamp relay control circuit, which energizes the headlamp relay.

CONDITIONS FOR RUNNING THE DTC
The BCM must be commanding the headlamp relay to energize.

CONDITIONS FOR SETTING THE DTC
^ The BCM detects a short to battery in the headlamp relay control circuit when the BCM tries to energize the headlamp relay.
^ The condition above must be present for more than 0.3 seconds.

ACTION TAKEN WHEN THE DTC SETS
The BCM stores DTC B2578 in memory.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC B2578 will clear if the BCM no longer detects a short to battery in the headlamp relay control circuit, after the ignition is cycled.
^ A history DTC B2578 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
^ The BCM receives a clear code command from the scan tool.

DIAGNOSTIC AIDS
^ If the DTC B2578 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ The following conditions may cause an intermittent malfunction to occur:
- An intermittent short to battery in the headlamp relay coil control circuit.
- The headlamp relay coil is intermittently shorted to battery.
- The BCM is intermittently shorted to battery.

TEST DESCRIPTION

Steps 1-7:

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 BCM is providing ground to the headlamp lamp relay. Indicating a short to voltage internal to the headlamp lamp relay.
4. Test for a short to voltage in the control circuit of the headlamp relay.