My new to me 2004 xa has code p0420. Autozone says oxygen sensor but I think they say that to everything. Anybody else got any ideas. It is running exactly the same as before I cant tell that there's anything wrong.

Thanks
Todd

 

Catalytic Converter. How many miles on the car?

 

This won't necessarily help you, but I have an 05 tC, with about 132K on it. At about 118K or so, I got the same code. I have an OBD II scanner, which gives the description for the code as well - 'Catalytic efficiency below threshold, bank 1'.
I reset it, and after a while it came back, so I figured it wasn't a fluke. I was told that was in fact the o2 sensor (top one is bank 1, there are 2), so I replaced it with an OEM one for $140.
Was fine for a while, then got the same code again. Reset it, and kept track of how many miles I could go before it came on again. It would go for 300 or so, reset. 700 next time, reset. Varied each time, sometimes a few hundred, sometimes a few thousand. I was up over 3,500 just this week, and it came on. Reset it, came back after only 45 miles. Reset again, on again after 50 or so this morning.
So I was fine with resetting every few hundred or thousand miles over the 13K since it first appeared, but now I'm going to have to figure out what the hell it is.
You could always buy a scanner on ebay for less than half the cost of the o2 sensor and reset like a ****, as I did.

Or if anybody has any idea what it might be, that would help us both out......

 

160k on the converter. I just had the engine replaced a couple months ago with one with 30k miles. I had run it with no problems for about 4000 miles and now it is constant.

 

Had this code on my tC. Cleaned the MAF sensor with CRC MAF cleaner and cleared the code. Code didn't come back for another 4 months, cleaned the MAF sensor again, cleared code again. Code came back 6 months later, repeated the process, now the code hasn't come back in 8 months.

I usually get the code after heavy rains and from what I've read, it's just the MAF sensor getting dirty from rain and dirt going through my CAI.

 

why does the catalytic converter go so much on scion? i know 160k miles is a good amount, but i've heard them failing before that. seriously i've had vehicles where the doors were rusting, the floor board rusted, and the wheels basically hanging off, and nothing else original still, but the converter from the factory.

 

How can you tell if the p0420 code is being thrown because of a bad code, vs, a bad o2 sensor .... Also, are there different codes for the primary vs the secondary o2?

 

Yes, there are separate fault codes for bad front O2, rear O2 and low efficient Cat converter.

 

Some info about that here: http://www.clubxb.com/forums/showthread.php?t=43131

 

That is wild .... I changed my cat a year ago. Is it even possible to blow a cat in 1yr? I am getting the p0420 code

 

How stock is your tC?

 

^well its not that stock but I put my own cat on ....it was a real good cat. Your thinking the cat is shot right? I am going to swap back to my stock exhaust soon anyway and I think i have a warranty for the cat somewhere

 

My thinking is that you need to look into the reason your converters go bad. And if you have any kind of mods that affect fuel system then that is probably it.

 

^nope - I am back to running the stock ecu for years now. That is what is throwing me right now ..... That is the initial reason why I was looking into how to clean my sensors because its hard to believe that the converter is no good

 

May be the cat you've installed was a lower quality aftermarket part. Did it have specific OBD2 approval cert?
Why did you need Walbro if you are all stock?

 

^ I don't want to say the company I bought it from but it was pretty high quality and I remember putting the warranty card somehwere. It was certified - The fuel pump was put in because I had long term plans for the car that I never went with.

 

A quality converter will have OBD2 approval stamped on it. Other than that any kind of issues that make the Check Engine light to be on or excessive oil consumption and use of race type of motor oil can harm it.

 

May not necessarily be the cat - I researched further, and found an exhaust leak can cause P0420. The differential between the bank 1 and 2 sensors as a result of the leak will throw the code.
Check the junction of the cat outlet end and pipe.

 

^ yea thats what i thought - I had my local muffler shop test for leaks and they confirmed there were none - I am prob going to let it be for now and take my exhaust off at the start of next year