I tries to fire up the auxilliary heater on my ML1 and no life was apparent. It says in the MB handbook the 'proper ' diesel heater will cut out at 1/4 tank but that is a different beast to mine which only comes on with the engine.. The LED light is not on so I dived into the various fuseboxs looking for why it is dead. No joy so I will try filling the tank up tomorrow and see what happen then.. I have never used it in battle before but if we are off the the East next week it might prove worthwhile to have.. Is there another reason I have not figured out????? The handbok are a nightmare to try and find out the technicalities as they seem to hold all the information to service centres who themselves have no idea what the stuff is.