Hi All
OK So P0420 Catalyst threshold exceeded bank 1

I will be tackling this soon and am going this way!
Software..if there is an upgrade which moves the parameters of the monitoring function then i will do this first to see what happens.
(the original OE cat passed emissions every time,however a gas analysis is not as accurate as a scope test across both sensors).

So i am presuming the rear O2 sensor is 'seeing' an oxygen content over time.this will according to data i have read start to happen when the rear O2 hits 625mv I.E oxygen seen coming out of cat showing incorrect conversion the rear O2 signal will react with a lower MV reading(presuming a correctly fueling vehicle and a correct cat conversion would have the rear O2 sitting at 800mv all day long).

So an air mass to front oxygen sensor test for responce with a scope will tell me the integrity of the injections systems fueling.

So if thats right i will do the following.

I will scope test the front sensor signal and rear sensor signal together and light the cat at fast idle and watch the responce of the rear O2 if a cat fault i will see the sensor lower to 625mv or lower.

wish me luck LOL.
ps..i have already carried out a smoke pro test to inlet and exhaust and all ok.

Let u know soon
Simon