A method is provided for monitoring an emission control device coupled to an engine. In one example approach, the method comprises, following a deceleration fuel shut-off (DFSO) duration, indicating degradation of an emission device based on an amount of rich products required to cause a sensor to become richer than a first threshold, the indicating carried out when DFSO duration is greater than a second threshold. The method also comprises an integration which is based on inlet air-fuel ratio, the integration starting only after a pre-catalyst sensor reaches stoichiometry.