My daughter just bought a VW Sharan from a dealer, and on the way home after filling it up with diesel the car wouldn't do more than 40mph, and the Engine Management Light came on. She took it back and the mechanic looked at it, said that there was a rusty connection on a brake light bulb, which would send a signal to the ECU and cause the problem. They fixed it fairly quickly, and it now seems fine.
Does this solution make sense ? I have had a similar problem with a Renault diesel and it was related to a problem with the Diesel Particulate Filter. Mine was fairly easy to sort out, but I know they can be expensive problems to fix, and am wondering if hers has got a similar problem and they've done a quick fix on it which will reoccur again.