P0420 Code Solved

I have a 2008 Toyota Prius, Like many here, I had the impossible dreaded P0420 Code. This is what I tried that did not solve this problem:

1. Changed both the upstream air/fuel sensor (a bitch to replace) and the down stream o2 sensor-no luck

2. cleaned the air/fuel sensor on the air box and cleaned the throttle body and air box! No luck!

3. Changed the spark plugs, and still no luck!

Every time I did something and reset, the p0420 would come back on after about 35 miles 3 times.

Finally gave up and went for an aftermarket Cat converter. What is interesting is that I live in NY State, which has adopted the California emissions standards. And that means you can't install an unapproved aftermarket Cat. And most aftermarket cat companies will not ship aftermarket cats to NY. I checked the NYS law and yupper that is right. So I went on ebay and found a company from Canada (First Choice Exhausts). Their 2nd Generation cat went for $108, plus $9.99 shipping and freaking 8% tax for a total cost of $128.50. And lucked out as they not only shipped it to me, it took only 4 days, evidently shipped out of Niagara Falls.

Anyways, took it to my mechanic who installed it pretty easily. First he removed the o2 sensor. Then he removed the bolts to the exhaust manifold, and cut off the old cat from the resonator and removed the spring bolts dropping the cat out. He slide the pipe from the new cat into the pipe to the resonator, placed the new exhaust seal on to the manifold, and bolted on the spring bolts. He then screwed the o2 sensor on. Rather then using the new pipe clamp, he did me a favor and welded the two pipes together. He lowered the car and I started it and no leaks -no problems. I erased the P0420 code. I have now driven the car over 400 miles and no check engine light. So obviously, the main problem with the P0420 code was the bad cat. This cat not only has a 5-year warranty, but is EPA approved.

Hope this info is of value to all you experiencing that dreaded #*%^@ P0420 Code!

I should mention that about 8 months ago, I was experiencing the P0420 code, but rather go through all the BS of spending money to try and solve the problem, I opted to buy one of those o2 sensor extenders. And that actually kept the P0420 code from coming back on until recently. That extender only cost $6.50 with free shipping. We are talking the downstream o2 sensor. So, if you want to go cheap and not F around with the cat, give the extender a try! Very easy installation you can find on youtube.

 

OK, I found out how to change the title! Thanks for bringing it to my attention!

 

Mine was just doing the cheap thing first when the P0420 code came on. What is interesting is that prior to this, about a year ago, the P0420 code began rearing its ugly head. So rather than going through all the BS of trying to solve the problem, I bought an o2 sensor extender, screwed that in and screwed the o2 sensor into the extender. erased the code and never came back on until recently. The o2 sensor was totally black with carbon build up, as was the extender. Replaced with a new o2 sensor without the extender (which was pretty rusty anyways) and erased the code, but came back on after around 35 miles. Erased the code once more and the same happened. That is why I finally gave up and bought an aftermarket cat. once installed, erased the code, and now have driven over 400 miles and no check engine light!

 

The upstream air/fuel sensor was already replaced a few months ago. This cat had about 220,000 miles in it. And nothing kept the P0420 code off short of a new cat which is working fine. My 2004 Prius had the same problem, so I used a cheater o2 extender so I could pass inspection. The extender worked great. This time I decided to do away with the P0420 nightmare with the new cat.

No codes anymore. But am thinking of getting 4 new ignition coils to go along with the new Iridium plugs I just installed. This time I went with the Denso #4701 Iridium TT (IK16TT) spark plugs and they work great!