B2578
DTC B2578
Circuit Description
The body control module (BCM) controls the headlamp relay by grounding the control circuit of the headlamp relay coil.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2578 Headlamp Control Circuit High
Conditions for Running the DTC
* Voltage supplied to the module is in the normal operating voltage range,approximately 10-16 volts.
* The headlamps must be ON.
Conditions for Setting the DTC
* The BCM detects a short to voltage in the headlamp relay control circuit or the low beam headlamp relay control circuit when the BCM energizes the headlamp relay.
* The condition must be present for more than 3 ms.
Action Taken When the DTC Sets
* The BCM stores DTC B2578 in memory.
* The SERVICE VEHICLE SOON telltale illuminates.
* The BCM activates the daytime running lamps.
Conditions for Clearing the DTC
* A current DTC B2578 clears if the BCM no longer detects a short to battery positive voltage in the low beam headlamp relay control circuit or the headlamp relay control circuit.
* A history DTC B2578 clears after 100 consecutive ignition cycles.
* The BCM receives the clear code commend from the scan tool.
Diagnostic Aids
* If the DTC B2578 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
* An intermittent short to voltage in the following locations may cause an intermittent malfunction to occur:
- The headlamp relay control circuit
- The headlamp relay
- The BCM
TEST
