I have calibrated this diagnostic before (p0420 &P0430) for a different OEM. But i am assuming VW also uses the pre and post 02 sensor to measure the oxygen capacity of the catalyst. Which is why the shop replaced the O2 sensor first. And there might be logic to not clearing the codes. The catalyst health monitor is a… » 2/04/14 5:06pm 2/04/14 5:06pm