Cummins ISB CM850 (2003-06) Fault Code: 281 PID: SID 126 SPN: 1347 FMI: 7 Fuel Pump Pressurizing Assembly 1 – Mechanical System Not Responding Properly or Out of Adjustment. A pumping imbalance between the front and rear pumping plungers has been detected.

Fault Code 281 will most likely come active while operating at a steady state loaded condition. At this condition commanded fuel pressures are highest and the pump’s pressure balance is affected the most.

If a high pressure seal has failed, pump head drain flow will be excessive. If a seal failure has progressed far enough, the engine may not start because of an inability to develop fuel rail pressure.

If the engine will not start, there are two indications that the pump head has failed:

1)The drain flow will be excessive. This can be measured while cranking the engine.
2)The pumping plungers are broken or mechanically stuck.

A faulty fuel pressure sensor signal due to a damaged fuel pressure sensor signal wire will cause the fuel pressure sensor to be inconsistent. This condition can cause Fault Code 281 to become active on an intermittent basis.

Possible repairs:

1)Repair or replace the fuel lines, suction filter, or tank pick-up.
2)Replace the fuel pump head.