check injection on dash/code p0651?

megane 1.5 dci sports tourer 2008. can anyone help with this,spanner light comes on,check injection comes on the dash message,splutters a bit,light may go back off for a little bit,but then comes back on with same message,it then stays on and then goes into limp mode,garage checked car,replaced boost sensor £141,problem came back few days later,now they reckon its my ecu because of the above code,which was there first time,can anyone give me any advice please as not sure what to do. thanks.