DTC 51

Programmable Read Only Memory (PROM) error (Faulty or incorrect Electronically Erasable Programmable Read Only Memory (EEPROM))

Check that all pins are fully inserted in the socket. If OK, replace PROM, clear memory and recheck. If DTC 51 reappears, replace engine control module (ECM).
Clear DTCs and confirm "closed loop" operation and no "check engine" Malfunction Indicator Lamp (MIL).