Rail Pressure Stuck at 120MPa / 17.4k psi

I’m looking for some advice on how to troubleshoot this issue. I was driving from TN to MI and towards the end of the trip all of a sudden my truck developed a bad surge and erratic rail pressure. After a few minutes the rail pressure stuck at 120MPa / 17.4k psi. It’s the same pressure no matter what RPM or throttle position. What I’ve tried so far is reflashing the ECM, replacing the rail pressure sensor, and replaced the rail pressure sensor pigtail. None of this made a difference.

Truck has an ATS dual CP3 controller and I have a Cummins FCA in the top pump.

Unplugging the FRP sensor connection does nothing to commanded or actual value. Unplugging either FCA also does nothing to commanded or actual value, but you can hear the engine/injector rattle so it’s definitely increasing rail pressure. All I can think now is to check continuity for each FRP sensor wire to the ECM, and if that’s good I would think it has to be a bad ECM. Anyone have the pin out for a 2012 6.7 and/or recommendations?

Ats controller?

Pull the belt off the second pump and plug the stock fca connection to the stock location cp3. That'll narrow it down to the 2nd pump/fca or the controller if it runs good. If not look at the stock location pump/fca or plug.

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Ok- looks like I got it. Two nights ago I switched the rail pressure sensor and it didn’t fix the issue. I tested the pigtail connection and didn’t have voltage to the signal wire with key on engine off so I picked up a new pigtail. Last night, thinking it was just the pigtail and not the sensor, I put the old sensor back in after I replaced the pigtail and didn’t run it with new sensor. Tonight I swapped in the new sensor and it idles at 7.5k psi like it’s suppsed to. The truck was giving some weird WOT surging issues in the weeks leading up to this so I think the wire was starting to come loose, and when I was wiggling things around trying to see if I had a loose connection it probably lost its connection. Two separate issues, and very annoying.