The dreaded P0420, is there a final solution?

[RDMII]

First timer here, but long time shadetree mechanic. I have browsed this site numerous times before with questions but this is one that I cannot ever get a straight answer on and have reached my limit on patience.

Cliff notes:

Friend's friend has a 2003 Matrix. Code P0420 came on at 82k miles. Dealer replaced converter assembly and both O2 sensors, charged full boat, she argued it and got it covered under warranty.

At 123k miles the code came back. Dealer once again replaced both sensors and converter assembly, charged full price, she paid it.

At 160k miles the code returned. She ignored it and continued driving, unable to afford the repairs again, until 176k miles when I was asked to step in. I read up for over a week on here and numerous other forums, called around to people in the industry, made every effort to determine the culprit. At 184k miles I replaced the converter with an Eastern aftermarket unit and the rear O2 sensor. Light went out, car passed emissions. I charged her very little on labor because she's in debt already with this thing and I felt bad that Toyota dropped the ball twice before.

It's now at 188k miles and the light is back on, P0420.

So seriously, why are these cars so prone to eat converters, or what is the magic fix that no one has found yet? She's ready to drive it off a cliff and I'm at a loss because I've never had to replace a converter on any car ever in 20 years of working on them and my 1992 Lexus, my brother's 1998 Camry, his wife's 1993 Corolla, and numerous Toyotas I maintain are all on the original unit. Surely there has to be a Toyota technician who browses this site who has seen enough of them to chime in the magic fix. From what I've read on here it's a toss up of parts, some work, some don't, some people get by for a while, others don't make it a week. I'd really hate to tell her after all this that there's nothing I can do.

[mikered30]

Yes there is a solution, get a new ECU or get it reprogrammed and stop going to that gas station. Does the engine consume oil?

Check this TSB to see if she applies: http://www.matrixowners.com/tsb/T-EG026-04.pdf

A new ECU with labor is about $900.

[RDMII]

I don't understand your comment at the 'gas station', but whatever. The engine consumes a small amount of oil which is typical for it's age, maybe .25 quart between oil changes. It leaks more than it consumes but that's another issue I've yet to deal with.

The dealer won't touch the car again without doing the converter assembly and both O2 sensors as well (I've spoken to three different dealers, none of them will assume the previous repairs were done correctly), so that's over $2k in work for a car that's currently worth maybe a grand more, she's not going to go that route and I don't blame her. There is no sulfuric odor either, the ECM may not be one of the culprit ones or it's possible they replaced it already during the first warrantied repair, she doesn't have the paperwork but I can check the part number to verify. This at least gives me somewhere to begin looking.

[ShawnM]

So its burning out the converter about every 20-30K miles. It sounds like its running a little to rich. A slightly rich mixture thats still still within the acceptable limits wont turn on the check engine light but will make the converter work harder and shorten its life. I would tell her to take it to someone that will actually diagnose it based on the the actual scanner data stream numbers rather than just throwing parts at it based on the code alone. While im sure the converter will need to be replaced again there is obviously another underlying issue thats causing it. With that kind of milage its hard to say whats going on without seeing the actual data stream numbers. It may be as simple as an ECM program update as Mikered said, assuming the dealer didnt do it already. Although if they did im sure they would have charged for it.