B2577

Diagnostic Chart:

Schematic:

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

CONDITIONS FOR RUNNING THE DTC
The BCM must not be commanding the headlamp relay to energize.

CONDITIONS FOR SETTING THE DTC
^ The BCM detects a short to ground or open in the headlamp relay coil control circuit when the BCM is not trying 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 B2577 in memory.
^ The SERVICE VEHICLE SOON telltale illuminates.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC B2577 will clear if the BCM no longer detects a short to ground or open in the headlamp relay coil control circuit.
^ A history DTC B2577 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

DIAGNOSTIC AIDS
^ If the DTC B2577 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent and Poor Connections.
^ The following conditions may cause an intermittent malfunction to occur:
- An intermittent short to ground or open in the headlamp relay control circuit
- The headlamp relay coil is intermittently shorted to ground or open internally
- The BCM is intermittently shorted to ground or open internally

TEST DESCRIPTION
The number(s) below refer to the step number(s) 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 LP Park fuse supplies power to the coil side of the headlamp relay.
4. Verifies that the Body Control Module is providing ground to the headlamp relay.
5. Tests if ground is constantly being applied to the headlamp relay.