Engine management light on

It came on today, it never came on when I was driving, when I turned the engine off, left for about 2 hours, came back and it came on then.

I was down Coventry and done 206 miles back home, car ran sweet, no spluttering or anything, idles fine.

Could a sensor be bust? I done about 410 miles this weekend and you can imagine....the cars turned brown, could the dirt have got to one?

Vagcom my best bet?
 
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