First of all I have to ask what does "no one can find the cause" actually mean ?. If the full resources of a competent Garage with expertise on GVs can't tell you what's gone wrong, then the chances of someone on here offering a workable solution, will be very remote. Conversely if the guy next door whose only ever owned new Nissans hasn't got a clue, then here's a thought or two . If you have a code reader, then the onboard diagnosis system should tell you what's wrong, but you'll need to