Here is a link describing PO 420 http://www.p0420.com/ with what to do about the code.

 

Check for exhaust leaks. Does your car sound different ?

 

Toyota uses a crazy high catalyst efficiency, somewhere around 90%. Lose 10% efficiency, off it goes. That far exceeds any of the remaining tailpipe smog tests. My guess is its still mostly good and the CEL is nothing more than a nuisance warning light. Can happen if there's oil consumption or the use of additives in the gas that are high in oil, Or.. it just happens. I capped my rear o2 off with a modified $6 spark plug non-fouler 3 years ago to put out the P0420 CEL permanently. At AAP or Autozone look for the "Dorman HELP! 42009" non-fouler. Drill one out with 1/2" drill bit. Take the rear o2 sensor off the exhaust, put the modded non-fouler on, then put the o2 with the non fouler back on the exhaust. Done. Light goes out in a day or so.

 

Magnate, car sounds the same.

 

Leakyseals, What I did initially was replace my plugs with NGK Laser Iridiums and switched out the 2 O2 sensors. I bought a OBDII code reader that read live data from Harbor Freights for $69.99. After it coded again, I ran the O2 sensor readings and saw that the rear O2 was wavering in voltage up and down.

Let me throw this out there: 2 years back, a local Oil Change shop adding one too many quarts of oil on my car. After driving it a day, the car started shuddering and barely got it on the driveway before she stalled. I started looking around and open my air intake box up and found oil in there. Had to take it to nearby Firestone and shell out $400 for new plugs, Oil, PCV Valve and injector service. Seeing how oil went different directions, you think this played any role with the CAT going bad?

 

If the cat was down close to 90% over the miles, an event like that surely didnt help and may have sent it below 90%. In some cases it can burn off, others it can't. May not have shown itself until recent warmer weather. You will see a bunch of threads on here in the near future for P0420's as the weather warms up.

The ECU uses the front/upstream o2 sensor to configure fuel trim and take initial pre-cat o2 reading for catalyst efficiency. The ECU uses the rear/downstream o2 sensor for a post-cat air reading only. A comparison is made, and if the efficiency is high, beyond 90%, no light. Closer range, below 90%, light. Waveforms you discuss are functionality, lazyness, etc. Depending on which sensor thats good or bad. Because of the functionality stated above, replacing the front/upstream/pre-cat o2 sensor is a good idea to rule out too much fuel overwhelming the catalyst. The rear/downstream o2 on the other hand should remain fouled and lazy to provide a wider range. Replacing the rear o2 makes the catalyst efficiency test more sensitive and the range smaller. And thats where capping it off, pinching its nose with a non-fouler fits into this. with the non-fouler in place the rear o2 becomes less sensitive, widening the range, increasing efficiency, poof, lights out.

 

I should ask this.. Assume you don't do a smog emission test down there anymore, your inspection relies on CEL codes only now correct? If so the non-fouler is all you need. Some day the cat may plug up, but IMO we are talking years as is my case. But I can't say for sure. You will know when a cat clogs, the engine will stumble and backfire at high rpms as the exhaust backs up.

and if your handy you can always try taking it off and cleaning the catalyst. Sometimes that works, sometimes no. But its cheaper than replacement.

 

If your cats are weak, the anti-foulers that leakyseals suggested will definitely work. I used them on my old (damn) Dodge Intrepid.. it saved me the $900 for new cats.

The ONLY reason for the rear O2 sensors are for testing of the cats. They do not affect the fuel mixture like the front sensors do. The anti-foulers work by moving the sensor up and out of the direct exhaust stream which slows down their reaction time (as if going thru good cats).

 

I took the heat shields off the headers and CAT. This is what I found.





With me still breaking free from the fear of working on this car (I also have a '98 Camry XLE which for some reason, I have no problem tearing it down because its my older one), and also not an expert on Catalytic Converters, would this be considered a burned out CAT or is this normal for an 06 to have this amount of rust on it? Keep in mind, the heat shield has no rust on it at all.