Cummins ISB CM850 (2003-06) Fault Code: 284 PID: SID 221 SPN: 1043 FMI: 4 Engine Speed/Position Sensor (Crankshaft) Supply Voltage Circuit – Voltage Below Normal or Shorted to Low Source. Low voltage detected on the ECM voltage supply line to engine speed sensor.

Low voltage on the +5 VDC supply line can be caused by a short circuit to ground in a supply line, a short circuit between a supply line or a return line, a failed sensor, or a failed ECM power supply.

Possible repairs:

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