Here's the scenario so far:

Got a P0430 code so I replaced the O2 sensor with a Denso model. Code retrurned a year later so I replaced the sensor again with another Denso. Code retruned within a month, so I took it to a muffler shop in town and they replaced the downstream drivers side converter. While he had that coverter off, he shined a light at the upstream converter and said it at least appeared to still be good. That was last week, and now today I just had the P0430 return.

Short of replacing the upstream manifold/converter, I'm at my wits end as to what to do next. Any ideas?

yes, replace the first CAT or check if there are any leaks there.

Have you had anyone with a scantool actually check what the fuel trims and sensor readings are for Bank 2?

I could be wrong here... but my gut feeling is the muffler shop was just throwing an easy replacement on to see if it will fix the issue.. If you haven't replaced your upstream converter/header that is more than likely your culprit.

I do second the thought on scanning the fuel trims across both banks just to verify but am leaning highly towards a failing/old cat. If you're not looking to have it replaced you could always try the O2 spacer/spark plug nonfouler route to get the sensor out of the exhaust stream a bit to reduce the amount of reading it puts out. Has worked fine for me for the past year. There is a recent active thread on this around here some where. This would work considering that your upstream o2 sensor is fully functional and isn't causing screwed fuel trims.


ps: as a side note... not that I'm a exhaust technician or anything... but shining a light up the exhaust to evaluate the condition of a catalytic converter seems far from the best way to determine if its still efficient enough to fall within spec of what your ECU is looking for..

I just went through this exact scenario. I first replaced both drivers side a/f and O2 sensors. Code’s kept coming back after a month or so. Ended up replacing the manifold/cat with aftermarket. Still didn’t fix the problem. Replaced the aftermarket manifold with oem and now the code is finally gone.