Error Code P0420

[Tyler2]

So about a month I had error code P0420 show up on my 2001 camry, I reset it and I thought all was good since it didn't come back on, well I thought too soon, it came back today. So my question is if anyone knows the most likely reason for this? I have seen some people say it is definatly the cat converter and others say it could be an O2 sensor. Seeing as none of these are cheap parts I don't really want to play the guessing game. So like I said if anyone has any suggestions on what to check and or how to go about checking it, that would be greatly appreciated.

Thanks

Tyler

[heartdisease]

You could swap you 02 sensors and see if the code follows them. The code usually specifies bank one or bank two.

[Tyler2]

Good idea, just not sure if they are interchangable. I believe they have different length cables on them. The code is saying bank 1, which is the upstream sensor, so am I safe in assuming downstream is bank 2? I may just order a cheap senor online and try that before putting $300 or more down on a converter.

[heartdisease]

Yeah maybe not hu, my brother in laws car had two different part numbers, the downstream sensor was more expensive also if I recall correctly. I guess a parts search could tell you if they are the same part number, so you would know. You might check around for the cat also, we have a shop in town that has a line of cheapo's you can usually get one for $100 - $150. I have heard that some vehicles will throw a code with the cheap ones although I have had two of them with no problems.

[rj2046]

Originally Posted by Tyler2

Good idea, just not sure if they are interchangable. I believe they have different length cables on them. The code is saying bank 1, which is the upstream sensor, so am I safe in assuming downstream is bank 2? I may just order a cheap senor online and try that before putting $300 or more down on a converter.

I thought that bank refers to cylinder bank, as in on a v6, there are 2 banks of 3 each. Each bank would have an upstream, and downstream sensor. I may be wrong though

[BMR]

V6 or I4 engine?

So are you getting *only* error P0420?... or is there another?

P0420 means the downstream sensor is not seeing the exhaust getting any cleaner after passing thru the cat. So the intent is to catch a bad cat. But if either the upstream or downstream sensors are reading poorly, they can cause a P0420 to be thrown.

You can check what sensor is used where here in Denso's online catalog. Be aware if it has CA emissions it might have air/fuel sensors instead of O2 sensors.

[BMR]

Originally Posted by rj2046

I thought that bank refers to cylinder bank, as in on a v6, there are 2 banks of 3 each. Each bank would have an upstream, and downstream sensor. I may be wrong though

Yes, bank = cylinder bank. There's only one downstream sensor, located just downstream from the cat. And there's two upstream; one in each exhaust manifold's down-pipe.

[coffee-3000]

For a V6, Bank 1, sensor 1 is the O2 sensor near the fire wall ( back of engine).
Bank 2, sensor 1 is the O2 sensor near the cooling fan ( front of engine).
Bank1 sensor 2 is the down stream O2 sensor ( under the car).

[Tyler2]

Originally Posted by BMR

V6 or I4 engine?

So are you getting *only* error P0420?... or is there another?

Should have specified, it is the 4 cylinder model and yes it is only throwing the P0420 error code.

It only has the 2 sensors so I might try and test them by the method outlined in my haynes manual but last time I tried that it didn't really tell me anything, which is why I am asking for more suggestions.

[fenixus]

if it's older than 100k miles then just get a new Denso OE one from ebay or amazon or Advance auto (with online discount codes) or Rockauto and go with troubleshooting from there.

check your part number here (looks for OE, not universal):
http://www.densoaftermarket.com/cata....php?part=o2sn

as I recall it's the one ending with 4137, usually around $50-70+s/h cheapest on ebay I think.

[Tyler2]

I tested both sensors today. The down stream one is within the specs for resistance and the voltage fluctuates between .23 to .35 volts so according to my manual thats good too. The upstream sensor however comes on at .29v and does not change, no matter how long the car runs. So unless anyone tells me otherwise, I am going to assume that is the problem and go ahead and order up a new sensor and see if that fixes it.

[fenixus]

I would replace them both. maybe the new upstream will fix the issue, as the computer monitors the cat by comparing the output of upstream (before cat) and downstream (post-cat), but anyways, the rear one is old and not so reliable (could be slow reacting).

it's a good practice to replace o2 sensors after 100k miles or AFR sensors around 150k miles.