Infamous P0420 CEL code

Hey guys. I popped a CEL the other day in my Tacoma. I scanned it today and it showed a P0420. I did a search and found a lot of results. Must be pretty common?

A few of the results suggested to check the o2 sensor's and the cat's. I waited for the truck to cool and crawled under it. I removed the rear o2 sensor first. I found this:



I figured it was just normal coloring. The truck has 106xxx on it.

After that I removed the front o2 sensor and found this:



Looks like it was replaced not too long before it was purchased. Sweet.

I have a stock exhaust (for now) and still have my cat's. I figure i'll replace the o2 sensor first and see if the code comes back. What do you guys think?

 

On Rockauto I found a few results for the rear o2 sensor.

-Denso universal
-Standard Motor Products
-Denso OE style
-Bosch OE type
-Delphi
-NTK
-Airtex/Wells
-AC Delco

Anybody have good or bad experience with any of them?

 

Denso OEM replacements are what i installed and have had good luck with them. our trucks seem to dislike anything besides oem replacements like Bosch or Denso, i wouldnt bother with anything besides them(especially a universal sensor). its hard to tell by the pics whether the sensors need replacing or not,they most likely do. to find out for sure youd have to break out the multimeter, or just replace em and see. hopefully its not your cats is all i gotta say though,they can be pretty pricey.

 

How do I test them with a DMM? That would certainly help make sure that the o2 sensor is the problem lol.

Yeah as soon as I saw 'catalyst' I sighed. Getting a universal one for my old MR2 was $120 and that was before 1/1/09. I wouldn't want to see how much they'd go for for my Taco.

 

you need one with continuity, take an ohm reading between the two black wires. Bank 1 sensor 1 should read between 0.8 and 1.4 ohms. a bad sensor will have no continuity. IIRC. i think you can also get obd2 code readers that are able to test this kinda shit to.

 

hey willtotheumm how many miles do ya have on your truck????

 

hey if it ends up that you do need a cat look into magnaflow they now have a blot on.... and I think Autozone has it for a bit under $400

 

RockAuto.com has some of the best prices when it comes to things like this, I would check them out too.

I've not found anything they couldn't beat the price on from one of the local auto parts stores. BUT...I only use them when I don't have to have the part immediately, since it has to be shipped.

http://www.rockauto.com/catalog/raframecatalog.php

 

Well I found an OEM style Denso for $65.71 shipped. Part number

$61 234-4189 Oxygen Sensor

234-4189.

The weirdest thing happened today. CEL was on on my way to work this morning, and on the way home 8 hours later. I relaxed at home and 2 hours later went to leave. No more CEL. Drove all over town and still no CEL. My mileage didn't seem effected either. Hmm...

The truck has 106xxx on it.

 

man I hate to say it but you may start thinking about the cat

 

^ why do you say that, because of mileage?106k isnt much at all

 

hi, just had a similar issue P0136 I blew both O2 sensors... turned out my exhaust manifold cracked. Cold air was being sucked in over the sensors and blew them, might want to also check for leaks. My rear sensor looked like coal. Hope this helps.

 

Thanks for all your help guys. But the CEL hasn't come back so i'll be paying close attention to it. Gas mileage is back to normal too.

I'm not sure if maybe a slightly shook something loose in one of the o2 sensors? Or maybe one of them has a loose wire? I'm not sure. But once the light comes back, if it does, i'll bump this thread with an update.

 

It's been a few months since your last post, did the light come back on???