Medium and Heavy Trucks
Have Truck Repair Questions? Ask an Expert
Here are the definitions of your codes.
46 is low oil pressure warning. This can cause RPM limiting if the ECM is programmed to derate.
39 is an injection actuation pressure fault. This does not cause RPM limiting.
31 is a loss of vehicle speed signal. This will cause limited RPM
49 is an inlet air heater fault. This can not cause RPM limiting.
51 is low ECM DC power supply. This can not cause RPM limiting.
If by change the fuel pressure is OK, I would next suspect code 31 or 46 may be active and causing your RPM to limited.
Let me know if you need more help. I am happy to assist.