this is exactly what happend to my arosa 16v, i took it to seat for a proper diagnosis and it came up break light switch and engine temp sensor, they replaced both and EPC as gone but Emissions light has come back on agian, so i took it back to seat and they did another diagnosis and this time they said it was a wireing fault that goes all through gearbox and cams and that they would need to have the car for two days, i didnt believe this however as it would have come up on the first test if it was a real problem surely? i think it may be lambda sensor but can they cause the car to throw up false codes?