Kwt660

One of our did that for a while. Possibly a sensor, but change fuel filter and try that.

 

So? You could have gotten bad fuel. It's a cheap filter to change. See if that works

 

have u found out what is causing the fuel rail pressure diagnosis--I have been having the same problem for the past year or so but truck performance has not been affected--problem only shows when I self diagnose the truck--have been to the shop several times with cummins for other issues and this code does not show up--has not affected anything

 

What model ISX do you have? If it's one with the common rail, the sensor is at the front of the common rail.
Another possibility... these engines are terrible for losing seals on the fuel pumps, and a lot of carriers will have to reseal the fuel pumps before the dealership(s) they're trading them in to will accept them. Well, they're trying to be as cheap about it as possible, so sometimes they won't replace the banjo seals where the fuel lines connect the fuel pump, and you get little bits of rubber which get into the fuel system... if the DTCs show issues with all six injectors, that would be a very likely culprit.