From Deere Tech Assistance, codes not in the tech manual:
Representation of the Message Displayed
Description of the Message
LoFUEL
The Fuel Gauge needle has gone into the red zone.
Appears only once during the power cycle.
tEnPHI
The Coolant Temperature needle has gone into the red zone.
Appears only once during the power cycle.
nEUtoF
Gear Tractors- The Operator is out of the seat and the transmission is in gear.
HST Tractors- The neutral wire jumper cap located under the left foot deck has been removed or is loose.
PtOOn
The Operator is not in the seat, the park brake was not set, and the PTO switch is on.
FPtO
The Operator is not in the seat and the Front PTO switch is on.
(EEC Only)
EnGrUn
The engine is already running and there is an attempt to start the engine.