Cummins ISM CM870 (2003-06) Fault Code: 387 PID: S221 SPN: 1043 FMI: 3/3 Accelerator Pedal Position Sensor Supply Voltage Circuit – shorted high. High voltage detected at sensor supply circuit for the accelerator pedal position sensor.

This fault is logged when the ECM senses more than 5.25 volts on the accelerator pedal position +5 volt supply line. This can be caused by a short circuit to a voltage source in the OEM harness or a short circuit to an actuator signal circuit that is greater than +5 VDC.

Possible repairs:

1)Repair or replace the OEM harness.
2)Replace the ECM.