2007 S3, drove 50 miles on motorway and CEL came on but there's been no loss of power. I know I need to get codes read to see what's going on but I would have thought it would have gone into limp mode?? I stopped and restarted engine a couple of times and CEL was still on. Only difference was I filled up with Shell Vpower Nitro+ for the first time before going for the drive (I normally use Momentum) - hopefully this was just a coincidence. Any ideas on what may have happened ?