Hi Declan

"We operate to try and help our customers and build relationships not screw them at every opportunity for the most expensive part possible. If a genuine cat is required it will be fitted and we all have built up our experience along the way with what to fit and what not to fit"

You pretty much summed up your predicament in that statement.

Your experience is being "built up" as this unfoulds & you are also still learning what to fit & not what not to fit.

Tony is correct (even if his posting style is less diplomatic than it might be )

The blunt reality is that you almost certainly have fitted a component, which is not fit for purpose (regardless of the manufacturers claims).

I don't think that I am alone in my view that, P0420 is one of the most accurate DTC's that we see every week.

Rarely does the conclusion turn out to be anything other than "Catalyst Efficiency Below Threshold"

This article is five years old now, but nowt has changed, as regard aftermarket Catalyst quality.....