Need help diagnosing a P0430 error code

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Originally Posted by BoxsterSenior

At idle and 180 degrees engine temp……….
BANK 1
Front O2 sensor voltage readings: 0.08 to 0.78 fluctuating (like roller coaster)
resistance reading: 128 steady (flat line)
Rear O2 sensor voltage readings: 0.68 to 0.76 steady (flat line)
resistance reading: 320 steady (flat line)
BANK 2

Front O2 sensor voltage readings: 0.09 to 0.78 fluctuating (like roller coaster)
resistance reading: 64 steady (flat line)
Rear O2 sensor voltage readings: 0.65 to 0.79 steady (flat line)
resistance reading: 192 steady (flat line)

All (4) O2 sensors heater voltage: 2.05 v

Observation: The front and rear O2 voltage readings for both Bank 1 and Bank 2 are almost identical and acting the same. However, the Bank 2 resistance values are approx. 1/2 of the Bank 1 values.
Could this be cause of the P0430 error code…….the O2 sensors rather than the pre-cat???
[no P0420 (Bank 1) codes observed]



Thanks, Phil

I wanted to bring this back to the foreground.

I have an '01 base 986. I used to frequently get the P0430 code, along with a couple of others, mainly the P0420. Not long ago, I got some new ones and finally took it to get fixed. I went to a very good German car specialist shop in Chattanooga, and they seemed to have sorted it all out. Both O2 sensors ahead of the cats were replaced, along with the oil level/temp sensor (I was getting the code for it being below limits). That work was about 3 months ago, and until a couple of days ago, no CEL. Then it came back, and it's showing the P0430 and P0420 codes again.

I hooked up my Durametric and cleared the codes, but I also took a look at the O2 sensor numbers.

Voltages on all four sensors were pretty steadily going up and down, mostly together. I thought one set (either ahead of behind the cats) should be a pretty straight line.

Anyway, the other numbers (resistance) are quite different now from before the work was done. Before the work, 3 out of 4 sensors showed a constant 64, and the one behind the cat on bank 2 showed a constant 128. That had made me think that one was bad, but that's not what the shop said.

Right now, the 2 ahead of the cats show either 64 or 128 (not necessarily steady), and the 2 behind the cats show zero. Constant zero.

What should the O2 sensor resistances actually be if everything was healthy?

Also, even though the OAS was replaced about a year ago, the shop told me it needed to be. Once I told them it was only about a year old, they kind of said never mind. The only symptom I get possibly from that is that it belches out white smoke on start up after the car hasn't been run for a week or so (I'm gone for work a week at a time, so that's a frequent situation.) The smoke stops after a minute or so.