Hello.
FE03 - communication error between LAS & FPS. The Las module is not receiving any data (battary capacity, operatting hours, FPS error code) from the logic board of the FPS via serial interfase (RS 232) of ribbon cable X20. If the ribbon cadle is OK, the FPS needs replacing.
Remark: If the battary is very low, this error code can also occur on acceleration or when a hydraulic function is selected (battary voltage breaks in briefly)
FE 56 - communication error between S-CPU & UWA-CPU.
Inernal fault in the LAS module. The two processor are no longer able to excange data correctly. (Replace the LAS module).

More shortly, prepare money for spare parts....