Hi, i would agree with les, fuel trim figures are a good guide to diagnosis, with no codes and good fuel trim figures and those gas readings it is almost certainly a duff or cheap aftermarket cat. On a recent snappy course we had a long and informative disscusion about aftermarket cats and the general opinion was that they are not yet up to scratch and can cause more headaches than anything else. we will only fit genuine now, especially on 2 sensor systems as cheap ones fail prematurely causing lost time, warranty claims and dissatisfied customers. steve.