P0420 CEL does not mean cat is bad on a V-6

[5 Speed]

I have the V-6 and have probably thrown the P0420 code a dozen times in the past two years and I have just reset it with the scan gauge. I just had my smog test today and here are the numbers.

HC (PPM) 1 at idle and 2 at 2500 RPM's
CO(%) 0 at idle and 0 at 2500 RPM's

With the Average for all vehicles of 17 HC (PPM) and a max of 100 allowed at idle and average of 13 with a max of 170 at 2500 RPM's I think 1 and 2 is pretty good. I did not even measure above 0.00 for the CO at idle and 2500 RPMs.

The reason I am posting this is I have read that a lot of people are having their first cats replaced and would really warn anyone of changing this out before getting a smog test.

If I could guess what throws the code it would be either a slight exhaust leak before or after the cat or somehow the O2 sensor is getting a little old.

[ddvk]

You may have faulty O2s... Check them out. If you have more than 80K miles on the original set, save up money for the new set.

I source my O2s from NGK Spark plug, NGK Spark Plug wire, NGK Platinum Spark plug for High Performance and Racing. (they are based off SoCal).

[5 Speed]

It has done this for the past 4 years. The California V-6 has a Air/Fuel front sensor and a O2sensor after the second cat. I have replaced the A/F sensor and will wait until the rear throws the dead O2 sensor. The second sensor is not involved with the closed loop function, just a check of the second cat so not a performance or pollution issue. I just wanted to post this because over the years I have seen quite a few post that they got this code and had to replace the first cat and the toyota price is over 1000 dollars. Some have done it under warrantee and some not, I would just suggest to get a actual test at the pipe before I believed the code. What is interesting is if the code is not cleared and the vehicle cycled to get a system ready reading, it would not pass smog in California even if it had perfect readings off the pipe.