replaced upstream sensor but PO420 bank 1 code still fires

An emissions test will confirm a bad cat. Removing the O2 sensor and inspecting the cat with a borescope will save you from disassembling the exhaust. Replacing the post cat O2 sensor will probably be the cheapest route, unless you have access to the right tools.

 

Hey op it could be the second cat I had the aNd problem and had to do the second cat and the sensors.... One thing about the sensors the seal that comes with it has to be place right even though it looks like its the aame on both sides one side is slightly different check it out the the thing is check the seal / gaskect out ya may just need that and not the whole sensor ......snap some pics of the sensors and put the up....... I'll try to do the same to show ya what I mean.....

 

Oh yea and rockauto.com beat deal on the sensors.....

 

You will most likely need to inspect both cats, but the theory of the first or "primary" cat being failed is not likely. If you look at the image below, and have access to the diagnostic information on Mitchell, it shows that the catalytic converter being tested for efficiency is part number 7.

 

Thanks for this diagram, printing it out now as I am having emissions problems again. This P0420 bank 1 code came up again. Do you think that code can still only refer to the rear cat?

 

What was your fix for this issue 2 years ago?

 

It was to replace the "rear catalyst" as shown in the above diagram "7" this kept the check engine light off for 2 years. Is it then likely that the unit failed so quickly? I know by Calif law, where my car is registered, the manufacture of this unit actually has to provide a 5 year warranty. I love my state! However I want to see if in it throwing a P0420 Bank 1 code again that there is no chance the "warm up catalyst" as shown in the above diagram object "1" need also be replacing. Is it just more likely my "rear catalyst" went bad again?

Also how is all of this affecting my fuel efficiency, if at all.

 

I just replaced both cats and sensors with magnaflow California grade cats and denso sensors. I think the best bet is to get the truck diagnosed so that way you can figure out if there is a deeper problem causing this P0420 code. But if the warranty allows you to send the 2 year old cat converter back and get a new one, then why not try that first.

Have you changed the front O2 sensor? What about the rear O2 sensor?

I was told that if the sensors are bad then they can cause the cats to also fail. I read that the sensors should be apart of regular maintenance and changed every 80k miles or so.


As for fuel efficiency, have you noticed any change? For me I went from getting 16mpg to 14mpg when I first got the P0420 code about a year ago. Since I replaced the cats a sensors my mpg went up to 17 for the 1st tank! I'm praying it stays at 17mpg or gets better.

 

Ohcrap good point, i'd be without a convertor in the period it would take to exchange it for warranty replacment. It was also welded in place, your thought on this?

 

I'd say the welded in place isn't a big deal, just need to cut where the welds are. Then you can see if that same shop would weld you a piece of strait pipe for now or maybe just drive with out the rear cat for the time being. Ask a muffler shop what the best scenario is for this situation.

 

Absolutely do not waste your money on a simulator. I bought one when I got the p0420 code and it did jack shiy. Urd told me it only works if you have a functioning o2 sensor and no cat. I changed out the second sensor and it fixed the problem. Just to add to the discussion my trucks an 02 with 2 cats. Its was originally purchased in Nevada. The trucks kind of an odd ball with DRL's and its a TRD with no abs.

 

Ok, so i had this problem where my truck wouldnt throw a code, i had powerloss, and the rpms would bounce up and down at 2k rpm rapidly, but i hooked up my diagnostic tool and it had a pending code of P0420 which was bank 1 below threshold. I pulled the section of my exhaust with the cats and pressure washed them out (cats are less than 2 years old) fixed my problem, code hasnt come back and it runs good again. To be honest i didnt think it was going to fix it but it did so give it a shot.