So back in January of this year I got the dreaded P0420 code on my 2004 4Runner (126k miles). Took it to autozone was told the usual. Took it to the dealer. They checked for sensor problem and determined one of the converters needed replacing. Cost was right at $1k.

Fast forward 10 months and I'm getting the usual lights and the P0420 code again at 150k miles. Could my new converter have really gone bad that quickly? I'm fairly pissed off by all of this for happening a second time in 10 months. I'm concerned that it's actually just a sensor problem and I paid for a new converter the first time for no reason.

How uncommon would it be for me to experience this so soon after supposedly having it corrected the first time?

Thanks for any feedback.

Wayne

Update:

Had the 4runner at the dealer. The service rep says that the 2nd bank (not the one that was replaced in January) has "failed". I peppered the rep with questions about what diagnostic tests they ran, etc. and she put me in touch with the service manager.

I asked the manager what are the likely scenarios I would encounter if I ignored these indicators and just kept driving it as is. He eventually admitted to me that I likely wouldn't have any driveability issues with it for some time and that perhaps a sensor would go bad before I started having real serious issues with the converter.

He also admitted that if it were him he'd wait on it as well, rather than spend $1k on fixing it. He said that there's a chance it could even clear up on its own, and suggested I stay away from ethanol treated gas, and use the gas treatment additive from time to time in the event I just got some bad gasoline.

What do you guys think of his response to my questions? Does this sound legit? My wife is a worry wort and still wants to get it fixed but I'm leaning toward leaving it alone.

If you really had a bad converter then the dealer should have also fixed the problem that caused the converter to fail. Converters just don't fail on their own, something else has to be wrong.

the dealer can test the O2 Sensors to see if they are still good (most don't, they just replace them). O2 sensors should he replaced every 100K miles (I am sure this will draw criticism). When replacing, replace both the upstream and downstream at the same time (I didn't and got a different code back until I swapped out the second).

Per ritual, every 100k I get new plugs, wires, O2 sensors and I clean the MAF sensor (didn't start ritual until check engine came on at about 115K on my '00 4runner.

If you are even remotely mechanically inclined, you can swap out the sensors yourself. They are plug and play and you only need a wrench.

Oh, and I forgot. Warranties on Emissions are using much longer than the rest. It may have been covered by Warranty.