we have a G400 despite having a full tank of diesel when the indicator in car shows approx half a tank the engine stops running does any member have any idea what is causing this problem


Arnie's picture

Re: help

If the symptoms  exist only when the tank is less than ½ full, then it may well be a variation of the known ¼ - tank problem.


There is a fuel bowl inside the tank, which holds the fuel for the electric lift pump (under the tank) to feed from. This bowl is kept replenished by the fuel return line (only about 30% of the pumped fuel feeds the engine, the rest is returned). The idea is to prevent fuel starvation when on inclines. Anyway, the internal return line is liable to come loose and hence the fuel-bowl empties giving the symptoms of running out of fuel. Typically, when filling the tank, above ¼, the fuel can enter the bowl by flowing straight over its top rim and so the issue only happens when less than ¼ full (when the bowl relies on the fuel return line to fill itself).


Some people have managed to re-fit the internal fuel-return line, with keyhole surgery, through the fuel-level sender access, under the rear loading area metal hatch.


The tank holds 96 litres, so by filling to the brim, you should be able to determine the accuracy of the fuel-level sender, by noting how many litres your require to fill.


If your fuel-level sender is inaccurate, check its earthing, else replace.


Also, other real possible issues could be organic/bio growth in the diesel, which will block the internal strainer in the tank.


You can access the strainer and fuel-pump by removing the rear protection plate, under the tank  (6xM6 screws, easy job).


I would:


  1. Drain tank,
  2. Remove (unscrew) strainer and clean (new O-ring needed to re-fit)
  3. Check operation of electric fuel lift-pump (under tank)
  4. Renew fuel-filter in engine bay, front of engine.
  5. Replace plastic fuel feed-pipes, between fuel-filter and main pump (they will give serious trouble sooner or later, particularly if still originals)
  6. Replace O-ring on fuel-pressure regulator (it will help)
  7. ECU, you can ignore if you don’t get random shut-downs of the engine.
  8. Run some Archoil injector cleaner through a tank of fuel (
Pistonhead's picture

Re: help

Does the engine start runing again if more fuel is added? 

Are there any DPF (Diseel Particulate Filter) issues or warning light illuminating on the dash?



gooch's picture

Re: help

Hi any fuel leaks at front end - engine ?

Sent pm - should you need advice

Can be many things, ive owned x4 400cdi models similar issues, need to know complete symptoms etc

Thanks gb

Jdring's picture

Re: help

Hi Judy.

Are you saying that you know there is fuel in the tank (full) and that the gauge is reading half full.  AND the engine stops at this point?

I am not aware of any electronics which will stop the engine, but it sounds like your fuel level sensor is faulty anyway. More background needed?

Nick123's picture

Re: help

Have you checked that there is fuel available and that the fuel is reaching the engine. In the past I have had dirty fuel clogging up the fuel filters.