Need help with P0420

Bummer... It's a bit early in mileage for this kind of problem and not sure what you can do short of replacement... There's some threads on here about cleaning attempts... And putting something in your gas tank to fix it seems pretty much debunked.

So if it's not an 02 senor issue or recent recovery from too much motor oil, you're kinda out of options... Of course maybe someone will come along and offer up a way to extend the end of your catalytic converter's lifespan?

 

I don’t know how your gas petal could get hard to push, it’s fly by wire. Basically a rheostat that sends a signal to a computer. Have you tried replacing the plugs and air filter, cleaning the MAF and the throttle plate? I would try that first and see what happens.

 

And clean the MAF also. About as close to a tune up as these cars get.

 

I replaced the cat on my 05 Prius at 312,000 two weeks ago (yes this is a true statement), bought aftermarket Bosal from Rockauto.
I had the P0420 code for about three years, squeaked through NJ inspection last year (an act of God when the light was off going through emissions inspection). I did have crappy uphill performance and my engine does consume some oil. I did the plugs, coils, MAF clean about 18 months ago, result was the performance and mileage better, but still had the code and CEL on. Since the cat change, the code is now gone, mileage appears better, but want to get a bigger sample size before declaring major victory.

 

I have the same P0420 code. Looking through the forum people have suggested that worn engine mounts might cause this problem as the engine rocks breaking the seal between the manifold (header? in the USA) and the down pipe of the catalyst.

Also with burning oil you could have a jammed open PCV dumping oil into the throttle body. I'm looking into putting an oil catch can between the PCV and the throttle body but I'm not sure on where the best place to attach it is. I'd look below the butterfly valve in the throttle body and see if you have a lot of oil. I replaced the PCV valve (and broke the end off coil pack 4 as I was too lazy to remove it. Don't be lazy. ooops)





nssdiver has his as above but I'm not sure where it's attached. I've ordered a catch can like this and I'm hoping I can figure out a way of attaching it.




This was in the gen3 catch can thread but off a gen2, wire wool used to provide a baffle.
Oil Catch Can, Eliminate that knock! | PriusChat


This oil could then be getting passed into the exhaust and poisoning the catalyst. My catalyst look pretty new. I live in a salt area so it should look bad but it's in good shape. People are saying they only last 30k miles or so if you don't fix the problem I would say that looks to be the case from my car. I have no history on it so It's all guesswork.

One thread did suggest "CataClean Liquid Science Petrol Hybrid Car Engine Fuel & Exhaust System Cleaner" but I've not used it yet, with the catch can in place it could be an easy fix if it removes the oil blowing through. I'm also going to try an engine oil flush to see if that can help the rings seal better as this was a recall on some later engines.

the ring problem

Toyota's engine flush:

I'm interested in any further opinions. If the cataclean is a waste of money then it will have to be a replacement cat but in the UK a full OEM cat system is £100 ($120-125) so it's not too bad, the back box looked worse than the cat on mine so got the back box for £50 but I'll risk the cleaner for an experiment if there's no data.

 

FYI: There's a not normal situation in dealing with '08 Gen2 exhaust gas re circulation system... Which is to say that the system doesn't exist in the same way as normal cars.. In a gen2 it's done via valve timing. I like that idea in that it makes then engine design more simple. It's also why I like Gen2 more than Gen3