Like so many older cars running converted to LPG also mine displays a regular MIL. The code is a "tiny" leak of the tank evap system P0441
I recently cleaned the code and then tried to get it back running on gasoline on a longer drive, just out of curiosity. It wouldn't come back for 200 km and I eventually changed back to LPG to limit the gasoline cost. After approx. 80 km the MIL was back on with my old friend P0441

Now I'm not sure about the logic behind this evap check. I'm still weeding out some minor issues, which means one of the 2 tank level sensors is drowned or has connection problems. That means my gauge shows exactly half the actual fuel level (display is really an exact average of both floaters).
Is there any logic in the evap check that judges the vacuum in the tank in relation to its filling level? Theoretically it would be logical, as a full tank needs much less leak air to repressurize than an empty one. So maybe my evap system is just checking against a wrong table value to judge for leaks?
Strange also that it only appears to happen at LPG operation.

Any bright ideas and brainstorming would be welcome to help prioritize checking of the evap hoses, the evap solenoid valve or the fuel level sensor as my next target.

 

I'm not an expert on the Jaguar PCM programming, but yes, evap diagnostics depend on fuel level as to when they run. The FSM states:

"The evaporative emission fuel vapor management system is controlled by the engine control module according to calibrated data tables."

Full Evaporative system monitor drive cycle conditions:

"Make sure the fuel tank is between one third and three quarters full (adding fuel will increase vapor generation; the diagnostic will not run if the vapor concentration is too great)."

The evap diagnostics for US-spec vehicles (and possibly other markets) functions off of a small pump mounted near the tank. This only runs after the vehicle has been shut off. It pressurises the fuel system and then the PCM can measure leakage based on pressure drop.

Not sure any of this is a help to your problem. I would suggest (1) you fix the fuel level sensor. (2) if the code persists, smoke check the evap system to find leaks. It may be as simple as a bad fuel cap. Or it could be a small leak at the tank, canister, etc.

 

... strangely though the MIL has disappeared on my way home after work today.
I don't trust self healing cars too much, but fuel levels are annoying anyway, so that will be my first.

 

Po 441 and naturally Check engine light are indeed coming back . I drove like 500km in total on 6- 7 occasions ,with filling up the tank twice.
Trying to find out where and what is wrong . From my understanding near purge valve is closed so not purging vapor into the admission