Thanks,

I will try it.

Try this

Install a completely full LP tank

Turn the keyswitch on, engine off

With the hood open disconnect the white connector at the bottom of the hood, it should be labelled X14

Reconnect after 2 secs

Turn the key off

Disconnect x14 again

Turn the key on

Reconnect

You sould read a full tank, the code should stop coming

This is a fuel sensor problem. Can be the wrong calibration or technical failure.
Your truck is LPG so, using Pathfinder, you should activate the LPG presure sensor.
Once, Linde had some problems with these sensors, so they issued some Service Information (I don't remember the number) concerning it.
As far as I remember, this required some calibration in Pathfinder window.