Upstream Llambda or coilpack. Its an emmissions warning light so will be a missfire causing unburnt fuel so the llambda brings the light on or the Llambda itself is buggered.
Go to a garage that does diagnostics (Not Renault) and get it plugged in. If it brings up a sporadic/static miss-fire, it'll be coilpack. If it brings up a Llambda fault, it'll be either of the Llambda sensors and it ill tell you which one.