2006 Dodge Ram 3500 SLT 5.9L Cummins

Won’t start, died on the road. Had code P2509, changed batteries, checked all fuses next to battery and they were good. Disconnected fan clutch harness and still doesn’t start but nor connector pin is corroded off, the code scanner shows 84 psi fuel pressure but I am unsure about whether this is accurate since the truck is not running. What would my next step be in diagnosing the problem?