P0420 comes back after CAT and O2 sensors replaced

Thanks everybody. I indeed purchased OEM O2 sensors from Toyota Dealer(online) and both sensors were installed along with aftermarket CAT. After a week of installation, my car has everything(monitors) cleared and it passed Pa state inspection. The problem came back after about 2 weeks of driving since then. The check light is back with P0420 code. The local exhause shop where I had everything installed could not believe my story and they kept saying that it was almost impossible to have CAT going bad like that, and they insisted that they hardly saw CAT defective(1 out of hundreds they installed, maybe). They asked me to provide the proof by going to Dealer and have it checked. If Dealer says CAT is bad, they will honor the warranty of CAT. I just cleared code this weenend, still waiting drive cycle is done. I will send it to dealer if check light is back, and keep you posted the outcome.

I had a code P0420, I'd use my scan tool to do some dynamic

ambiguous advice from the

Just came from Toyota Dealer, CAT is found "not operating properly" and need replacement. So, I think that the aftermarket CAT is indeed a bad one. The local exhaust shop was recommended by our local Firestone auto shop and I paid only $157 for CAT(including the labor, not including the O2 sensors). Now, I am wondering whether the CAT is too cheap to function properly? what will happen to next one? Local Midas auto shop asked

it was a good move for me at first place. I can not decide to ask money back from the exhaust shop and go somewhere else or just go ahead and ask them to install a new one under their warranty? Any adivce?

harness.If I had a code P0420, I'd use my scan tool to do some dynamic

ambiguous advice from the

As I've mentioned many times and contrary to what some others incorrectly think, it is just about impossible to have a false P0420 code due to a bad O2 sensor #2, so the most likely cause is a bad catalytic converter.

One of the primary "ingredients" in a catalytic converter is platinum, which is one of the reasons why a catalytic converter is so expensive. The only way I can think of to get a cat that much cheaper than an OEM one is to use a lot less platinum. In my opinion, in the case of catalytic converters, you get what you pay for.

My advice depends on how much longer you intend to keep the car. If you are only going to keep it for 3 years or less, then go back to the place that installed it and ask for a replacement under their warranty. If you are going to keep it for 3 to 5 years, then go to a place like Midas, and if you are going to keep it longer than that, then get one from a Toyota dealer.

Thanks for the clarification, I knew that. I was only responding to what appeared to be a statement that only codes are scanned. In CA, codes are scanned and there is the sniff test.