Cummins ISM CM870 (2003-06) Fault Code: 284 PID: S221 SPN: 1043 FMI: 4/4 Engine Speed Sensor Supply Voltage Circuit – shorted low. Incorrect voltage detected on the ECM voltage supply line to the engine speed sensor.

The ECM monitors the voltage level on the engine speed sensor +5 volt supply circuit. If voltage falls below a calibratible limit then this fault is recorded.

Possible causes:

1) A short circuit to ground in the engine harness, sensor, or ECM.

Possible repairs:

1)Replace the engine speed sensor.
2)Replace the ECM.
3)Replace the engine harness.