Calling all P0420 Experts

The Tacoma is consistently throwing a P0420 error code. When driving in 4th or 5th gear at low RPMs with light throttle/load, the code appears. I'm hoping that someone recognizes the parameters at which the code is thrown and knows which cat and/or O2 sensor solved the problem. (All of exhaust is OEM).

Thanks for any advice.

 

I vaguely remember that you can check the reading in the sensor. If both produce stable reading it's probably the cat itself. Please correct me if I'm wrong.

 

I'm dealing with the same issue. I cleared it Sunday and an waiting for it to return. Grovestreet is right, you can check the resistance across the O2 sensors, if they check out, then either an exhaust leak or bad cat.

 

I had that code recently because of an exhaust leak at the gasket between the 2nd cat and the catback exhaust. Replacing the gasket took care of the code and it has not come back. If you don't have an exhaust leak then your back to the o2 sensors and cats