Hi everyone. I just got a P0420 "Catalyst Efficiency Below Required Level" code today.
Now, if I understand correctly how this works, is that there is an 02 sensor before the cat and another one after and the PCM analyses the different readings between the two, and that's how it gets its "Catalyst Efficiency" reading, right?

I do not smell any anti-freeze and no oil is buring, so it is unlikely that the cat got contaminated. The O2 sensors have not been changed for at least 70K miles.

I'm leaning towards the O2 sensors first and if that doesn't work I'll change the cat.

Does anyone have any opinion/advice?

Zero experience on a P0420. Here's a little info:

http://dodgeforum.com/forum/dodge-caravan/41553-p0420-dilemma-1999-caravan-expert-help.html

http://www.obd-codes.com/p0420

Thanks, RIP. Good info, as always. I have a feeling that the cat will need to be replaced.

Alphabravo I had a P0430 code (which is the same as a P0420 just different bank) I watched the upstream 02 sensors whle driving at 55mph and found that the sensor was lazy. Replaced the sensor and have not had the code since that was about 5k ago. A heck of a lot cheaper than the $1200 for a replacement pipe with the cats.

good luck

Thanks, Tempfixit. I probably should change the O2 sensors anyway, so I'll just change them first and then see what happens. I'll try the upstream sensor first. Thanks again.

Thanks, Tempfixit. I probably should change the O2 sensors anyway, so I'll just change them first and then see what happens. I'll try the upstream sensor first. Thanks again.

I have seen the P0420 on 2 different caravans, one with about 100k and the other one with 225k and after replacing both sensors, the code went away and didnt come back. Funny how the computer thinks the converter is bad and not the sensors.....

My understanding of this is that when the car first starts and is cold, the computer sees that the readings of the before and after sensors track together (Part 1). Then, after the car warms up and the CAT starts doing its job, the reading of the two sensors diverge (Part 2). The efficiency test failure indicates that they are not diverging and implicates the CAT. I also heard that you can take an inefficient CAT off and soak it in a mild detergent and rinse it off good and put it back on and it may work fine after that.

Thanks for all the replys. I got a lot of good info. I'll start by changing the sensors first then post the results.