Whilst driving down the motorway yesterday my engine warning light came on on my 2004 C270 cdi , it lost alot of its power and went into its limp mode , because it was Sunday and no garages where open I disconnected the battery and left it for 5 minutes then reconnected it and the car was back to normal with no light on and had regained all its power. I drove about 5 miles in it today and the light came back on but it did'nt lose any power it just kicked a load of black smoke out when I accelerated away from the traffic lights , I took it to a garage near me and the mechanic connected it up to his fault reader and it came up with something like turbo by pass circuit low , the mechanic advised me to take it to a Merc main dealer. Does anyone have any idea what could be the problem. Ive only had the car a few weeks and cant really afford to pay main dealer costs.