Running out of ideas on how to solve my P0420 code, need suggestions

[arcteryx]

I thought I had this fixed. This is the "Catalyst System Efficiency Below Threshold (Bank 1)"

I have done the following

1- replaced both O2 sensors on Bank 1 using Denso
2- replaced PCV valve with OEM unit

I am not convinced the cat is the issue. And don't want to throw $2000 for a set of cats, that's aftermarket money

What else can I check? I have a scangauge so it doesn't plot graphs. I wouldn't mind getting either a OBD2 gauge or, ideally an OBD2 wireless adapter to work with my iPhone. Does anyone recommend one?

With one of these, I could see the cat efficiency live to determine if the cat is the problem.

Open to other suggestions.

 

[bctlex]

In our 2001 Sequoia, which has 4.7L engine, we get the same error. Took it to dealer for diagnostic, they said there is a crack on the exhaust manifold which mess up the reading by the oxygen sensor and make the computer think that there is a problem with the cat. Their recommendation is to replace the exhaust manifold. I dont know if this would fix it. We sold the car without fixing it. The buyer knows it has this problem. The car runs fine even with the error. Hope this helps.

Chris