isx12 cm2250 fuel pressure only builds if injector harness is disconnected

[Signature620]

Have a read of the fault information for FC272. It reads a lot like this thread.

Code
Fault Code: 272

PID(P): S126
SPN: 1347
FMI: 3/3
Lamp: Amber

Reason:
High signal voltage or open circuit is detected at the fuel pump actuator circuit.

Effect:
Engine may run rough, may stop running, may not start, or may be difficult to start.



You have an open circuit or short circuit in the fuel pump actuator or its wiring.
The ECM disables the fuel pump actuator driver as soon as it detects this fault so you'll need to let the ECM power down each time you want to recheck if it's still active.