hi all i have a 1.4 16v Renault modus ?

hi im matt the other day on the way home from work i was having a eco drive pushing 46 MPG+

and then the EML came on and the dash read check emissions

now even after the dreaded EML had came on my avrg MPG kept on going until it settled on 48.8 MPG

so here's the thing with no misfire no loss in power HOT/COLD no loss in economy or any sign of a problem at all what could be wrong what sensor would i be best checking first

and will driving it cause me massive problems