Fault code: P0420 Catalyst System Efficiency Below Threshold (Bank 1)

I got the dreaded check engine light this weekend. I have an OBD-II bluetooth scanner with Torque so I was able to check it and clear it, but I am concerned about it. It hasn't come back yet after a week of driving. My truck has 135k miles and I don't think any work has ever been done to the catalytic converter system. The only recent changes I have made was putting a little bit of Marvel Mystery Oil in the gas (it was mixed into a gas can I had on hand).

Should I be taking my truck to a mechanic to check out the cat system? Sounds expensive.

 

This picture just felt so appropriate. I had the same code but it turned out that the previous owner of my truck gutted out the cat. But crawl under the truck and check the exhaust for leaks around the cat and test your o2 sensors. Dont give up man save your money and do some trouble shooting first. You may have to replace your rear cat like I did but you can grab one from rock auto for around 150$ If the bolts are rusted up real bad take an angle grinder to 'em and tap out the bolts and buy some new ones from a hardware store (dont forget to put some anti-sieze on the threads). The gaskets they send you aren't sufficient for sealing the flanges so you'll need to pick up 2 of the right ones from autozone (part number 61039)

 

nope

at around 135000 miles, o2 sensors and a/f sensors croak. most likely problem right here.
they do not last forever. my 99 4runner had exact miles and code...lots of other people too...
likely the sensor itself needs replace. cat could easily last past 200,000

I'd say replace sensor, reset ecu, and then next thing to die will be the front a/f sensor
in the next months

 

Do yourself a favor, as I had this code on my old 04 4cyl... If you buy an O2 sensor, go to rock auto and get the Denzo sensor. That's what toyota uses. If you go with another brand, you risk the light coming back on and buying another sensor. I replaced mine and it never returned, but of course I had it diagnosed at my shop for free to be sure that's what it was (benefits of working at a dealer)

 

What I gather from this is its most likely an O2 sensor problem, and if the sensor is bad it will trip the light again later down the road. So until that happens I need not worry. Sweet!

 

its probably the O2 sensor after the cat.

 

The check engine light has come back twice in the past month and I finally have time to check it out this weekend. I am not familiar with how to test the O2 sensors - is this possible without simply buying new ones? They are about $120 each and my fault code did not specify which is bad.

I found this link which has a great writeup if anyone else has to replace their O2 sensors.

http://www.lieblweb.com/o2replacement.html

Mine appear to be very easy to get to, and I've started saturating the bolts with penetrating oil to make them easier to break free.

My only concern is that it may not be a sensor at all since they aren't called out in the OBDII code. I am considering going to a mechanic to get a proper diagnosis.

 

Cat efficiency codes are generated by the rear 02 sensor. They are easy to change and can be found quite a bit cheaper than $120 if you look. Rockauto is a good source. I just replaced my rear sensor on my 96 for the same code and I bought a Denso sensor for $40 shipped on eBay. It would have been another $12 or so shipped from Rockauto.

 

Nice. That is the reassurance I needed to handle this myself. I was having trouble finding time to get into the mechanic anyways.

 

That is a great write-up and I now its stupid that you cannot go to a parts store and let them check the code, it would be great to know before you ordered the parts. BUT 120 each seems a bit high. Please take the time to check prices on RockAuto, that where I get lots of stuff for my truck, I got mine last year, and I think they were 61, or so each, and you need to get the DENSO, cannot stress that enough. I dont know the mileage on your truck, that play in on this, but mine had 177,000 when i did mine, it was the second set, since the wires were not in the factory set holddowns ( a halfass job) mine was not throwing a code but since I am taking my time and going over everthing, it keeps me busy. the pic of them really does not show how bad they were, these were the worst I have ever, ever replaced, I still have the special socket to remove them without cutting the wires, the old days, anyway on both when I removed them they were covered with black carbon and it fell off and broke up. these things wear out, and it makes your cats work harder, and it effects your mileage, which improved on mine.

 

Makes total sense. I'll take a pic of my sensor this afternoon, it looks really really easy to do. Just a little muddy from some fun in the rain last week

My truck is at 138k, which is why the post about replacing them at 135ish really rang true with me lol

 

What part number do I need? Is it the NP2344162 ? Where is a good place to look up part numbers

 

Had same exact issue link. I checked for leaks around the cat, but didn't feel any. So I switched from Kroger gas (high ethanol content) and that solved the issue for several months. Finally I replaced the O2 sensor about 7 months ago and haven't had the issue since. (I normally get parts from Rock Auto, but I got a better deal from Advance Auto with the coupon codes on Retailmenot.com.)

 

http://shop.advanceautoparts.com/we...#fragment-2?cm_mmc=ET-_-Trans-_-RAF-_-General

Yea I've only cleared it once on my own, the other two times it came and went. I fuel up often and always a different place so I'm sure the slight differences in fuel explain that. I'm looking at this sensor above for $90 on advanced auto, I will shop around for price, but the harness is listed as 36" long-is that right? Seems huge.

 

on my '01 the rear o2 does have a pretty long harness because it runs along the frame and then up into the cab, ending under the passenger carpet IIRC

 

Add $10 and u get $40 off http://m.retailmenot.com/view/advanceautoparts.com

i just used that one on a battery the other day. Compare and go with whoever has the best deal.

 

Hi people how would i know which of the two sensors i need to replace to fix this code ?