Cummins ISM CM870 (2003-06) Fault Code: 187 PID: S232 SPN: 1080 FMI: 4/4 Sensor Supply 2 Circuit – Voltage Below Normal or Shorted to Low Source. Low voltage detected at the sensor supply number 2 circuit.

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

During the fault code response test outlined for each sensor connected to sensor supply number 2, Fault Code 187 must be active before unplugging each sensor. If the fault code is not active, but can be easily duplicated by operating the engine, the following can be performed:

Operate the engine under the conditions that will cause Fault Code 187 to become active, even if it logs for a short period of time. Unplug one sensor at a time until Fault Code 187 stops logging under the test conditions. Each sensor can be unplugged with the engine running. Note: The engine may not start if the camshaft position sensor is unplugged.

Possible repair:

1)Replace the camshaft position sensor.
2)Replace the intake manifold pressure/temperature sensor.
3)Replace the EGR valve position sensor.
4)Replace the EGR differential pressure sensor.
5)Replace the rail fuel pressure sensor.
6)Replace the exhaust gas pressure sensor.
7)Repair or replace the engine harness.
8)Replace ECM.