P0420

Ok, new here so bare with me. I have a 2005 DC trd 4x4 4.0 v6. I have spent 3400 on head gaskets and a week later I had a p0420 code pulled. Dealer said to put a cleaner through it and see if it comes back. It did.... no performance issues then. I took to another deager and they said both sensors were working and it was the cat. I found out later I had 4 cats..... I replaced the drivers side manifold/cat. Still having the issue. I am having performance now. Chugging and such. Can anyone help? Do I need to punch out/replace the back cat? Is this an o2 sensor? Airflow? Any recommendations how to keep the cost down to fix this? 194k on the truck... trying to save by doing ityself but lost on the easy way out. Any help is appreciated

 

Welcome to TW. The rear cats have no sensors, so only the front manifold cats would throw an error.

P0420 means that the cat is operating below efficiency on bank 1, which means cylinder 1 side, which is the passenger side. So it sounds like you replaced the wrong cat.

Another cause could be a failing O2 sensor, which would be the sensor after the cat on the passenger side, but it sounds like the dealer ruled that out.

 

Interchange oxygen sensors ( both located after cat. If you get 430 and not 420 then your problem is the oxides sensor.

 

Wow! Am I that bad? I appreciate the honesty. So before I buy another cat... so there a difference between a bad sensor and a cat code?

 

Wow! Am I that bad? I appreciate the honesty. So before I buy another cat... so there a difference between a bad sensor and a cat code?

 

Some relevant reading:

http://www.easterncatalytic.com/education/tech-tips/the-misleading-nature-of-the-po42o-code/
http://www.aa1car.com/library/o2sensor.htm

So yes there are O2 specific failure codes. Also interestingly "If you determine that the O2 sensor is lazy, remove it and check it for any type of contamination, usually by oil or antifreeze..." It might be worth investigating since you did have head gasket issues which could leak coolant/oil into the cylinders.

 

Thanks! I have a new part coming friday... will post on the progress!

 

sub'd

 

any new info on this problem??

 

I got my second cat and will be installing today *fingers crossed that it fixes it"

 

how much was the cat??

 

Update!
2nd cat installed... about 800 vested... 400 each.

Still having the issue and a P0420 pulling..... both cats were the front. (Manifold to back cat)

Suggestions on what could cause this? I was told the sensors were functioning, but the code pulls from only the front cats....

 

Did you cross sensors?, that an easy way of checking if you have a bad sensor because you'll get a p0430 instead of p0420.

 

Have you checked for leaks yet?
I would try re-torquing the manifold nuts to start.

 

I had the identical code come up last year. For me it ended up being the passenger side front cat, but you should always ALWAYS replace o2 sensors first, since they are only $50 a pop. I would put money that it's just a sensor and you could have fixed this in the first place for way less. In my opinion there's really no other Thing it could be, except possibly a MAF sensor, which is think would be a different code.

 

working on this same P0420 code. will try swapping front sensors and see if 430 pops up instead. may just replace the front sensors since I have heard they give out. thank you crashnburn80 and sprockethead.

 

How about something like this: http://m.ebay.com/itm/112096774197
Or weld a new O2 bung after the 2nd cat.

 

Replaced the Right and Left Side upstream and down stream O2 Sensors and the truck is doing well. Gas Mileage went up a few mpg as well. I suspect the original sensors were not doing their job very well.

 

11yrs on the job, sounds like they did well to me

 

Why does this truck need 4 cats? Is the engine that dirty?