Code P0420, Cat or O2 sensor?

[mybenje]

I have a check engine light on with code P0420 on bank1 on my 04 4 Runner V8 with 90K.
My question, did anyone go though this before? and what was it? I have heard that most likely it is the O2 sensor, but my Mechanic said that he tested all O2 sensors and they came back in range, he wants to replace the cat which can be expensive,

I am in California, which makes me more expensive. Any input would be appreciated,

 

[ARK_SWAMP_RIDER]

Not too sure on your 4runner, but I'll share some info on my old car. I had a 96 Ford Mustang that had the P0420 code. That's a universal emmissions code I believe. In my case, the car didn't have cats and that caused the problem. It was nothing to do with the oxygen sensors. You're catalytic converter isn't doing its job. On my car, I rigged up a spacer so that the oxygen sensor didn't actually stick down into the exhaust, thus it got a lower reading than the front sensors and it did away with the light. I can post some info on that if you'd like. However, I'm afraid that with you being in CA you'll have to do the expensive fix to pass emissions (I'm not familiar with their system, but hear it's a pain).

 

[toto]

The complication is that the sensors are what tells the computer whether or not the cat is working properly. If the sensors aren't right, then the computer could be tricked into thinking the cat is the problem.

Found a link to this article on another site.
http://www.alldatadiy.com/techtips/2006/20060131c.html

 

[ARK_SWAMP_RIDER]

While it is a possibility that it's the sensors, the fact that the symptoms also fit the cats and that he had the sensors tested which came out fine. For about $5 in parts and a little of your time, you can build some spacers that'll probably help determine the culprit. It'll bring the sensor out of the exhaust. If it's the cats, this'll turn the code off. If it's the sensor not working properly or an exhaust leak, the light will remain on.

 

[mybenje]

Thanks guys, this helps a lot. I will talk to my Mechanic and report back. This forum is a great ressource.

 

[ToyTech99]

Not too sure on your 4runner, but I'll share some info on my old car. I had a 96 Ford Mustang that had the P0420 code. That's a universal emmissions code I believe. In my case, the car didn't have cats and that caused the problem. It was nothing to do with the oxygen sensors. You're catalytic converter isn't doing its job. On my car, I rigged up a spacer so that the oxygen sensor didn't actually stick down into the exhaust, thus it got a lower reading than the front sensors and it did away with the light. I can post some info on that if you'd like. However, I'm afraid that with you being in CA you'll have to do the expensive fix to pass emissions (I'm not familiar with their system, but hear it's a pain).

How many miles are on your 4Runner? The cats are covered for 8 years/80,000 miles as dictated by Federal warranty law.

 

[mybenje]

I have 90K, I was aware of that, I have tried with the dealer and Toyota with no luck,