P0420 - try the O2 sensor first?

[basil]

I've got a 96 Camry with the 5SFE four cyl with 113k miles. The check engine light comes on from time to time, and shows a P0420 (catalyst efficiency below threshold). Once I clear the code, it'll take it 2-3 months to return.

My question is this: it seems that the rear O2 sensor is the most likely culprit, considering the mileage on the car (low for its age, but more than 100k) and the fact that the light stays off for a while. It seems that if it were the catalytic converter, the light would come back on much faster after being cleared.

Is this correct, or does something thing the converter is the more likely cause?

Right now, I'd rather not replace both the converter and the rear sensor.

Thanks.

[new echo owner]

I would suggest having the cat check first before replacing anything. Contrary to popular practice of replacing O2 sensor, they actually don't go bad very often since the post cat O2 is working very minimally comparing to the pre-cat sensor. You might have a cat that is on its way out, and the sensor is just doing its job of alerting you to the problem.

N.E.O.

[basil]

Does anyone have the OEM Toyota part number for the catalytic converter (the one under the car) for my 96 Gen 3, 4 cylinder, non-California model? The online parts places aren't showing me what I need to see.

[JohnGD]

Sure, by 100K miles these wear items (oxygen sensors) should be replaced.

It's better to verify the cat performance like in emissions check. But generally if the engine is well tuned, there are no air leaks or exhaust leaks upstream of the cat, then I'd suspect the oxygen sensors first.

I'd recommend Bosch planar types. These are more resistant to contamination than older thimble types:

http://www.boschautoparts.com/Produc...nsors/PlanarO2

Originally Posted by basil

I've got a 96 Camry with the 5SFE four cyl with 113k miles. The check engine light comes on from time to time, and shows a P0420 (catalyst efficiency below threshold). Once I clear the code, it'll take it 2-3 months to return.

My question is this: it seems that the rear O2 sensor is the most likely culprit, considering the mileage on the car (low for its age, but more than 100k) and the fact that the light stays off for a while. It seems that if it were the catalytic converter, the light would come back on much faster after being cleared.

Is this correct, or does something thing the converter is the more likely cause?

Right now, I'd rather not replace both the converter and the rear sensor.

Thanks.

[1996camry]

I am not claim to be an expert on P0420 bank1. This weekend I got CEL (Engine Check Lignt) with code P0420,too. I removed the sensor on bank 1, and I deep the sensor inside a cup with small gasoline . I hold the sensor 1-4 mins. inside the cup to allow the dirt releases from the sensor. Repeated 1-4 times then wipe with clean napken. make sure you wipe really good (dry) before you installed back on bank1. Now, I installed the sensor. I reset CEL by remove the negative battery terminal. CEL has not came back for 3 days

If you wonder, my catlalic converter had been changed about a year ago with an aftermarket.