I had CEL over a year ago - dealer 'fixed it' and it stayed off for many months. Came back a couple of months ago - dealer looked again and said it was most likely a temperature sensor but intermmittent (I agree it was intermittent). Eventaully fault came on fully and light would no longer go off by itself. Dealer looked again and found two problems: sensor on a turbocharger and fault fuel filter heater. Both replaced under warranty and fault now clear. Car's performance in very low temperatures is also definitiely improved
Peter T