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Old 01-30-2013, 12:09 PM   #1
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Need help diagnosing a P0430 error code

My 01 Boxster ‘S’ Tip (69,000 miles) has started to throw P0430 codes about every 200 miles this winter. I have read from previous postings that “generally” the P0430 indicates the Bank 2 pre-cat is not functioning properly, as determined by the front and rear O2 sensors. My question is it the pre-cat or the O2 sensors, or something else?
With my Durametric reader I collected the following readings after a 10 mile normal drive.
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]

ADDITIONAL Durametric reader information…
Ready Status….
Cat Conv Effectiveness …………………………Pass
Fuel Tank Ventilation ……………………………Fail (no explanation)
Secondary Air System …………………………Pass
Oxygen sensors …………………………………Pass
Oxygen sensor heaters …………………………Pass

Would the fuel tank ventilation (fail) have any effect on the P0430 code?
Fuel cap about 2 years old….seal looks good?

Also, MAF cleaned 200 mile ago.
Any and all suggests will be welcomed.

Thanks, Phil

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Old 01-30-2013, 12:25 PM   #2
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I don't know enough to comment on your O2 sensor data, but I do have a clarification question for you on the fuel ventilation reading.

Have you recently used the Durametric tool to clear the fault codes? If so, you may be getting the "fail" status reading simply because the systems haven't cycled enough for the fuel ventilation system to begin monitoring once again. I had cleared all the codes in my 01S and saw a similar fail reading. After driving the car for several more days, the fuel ventilation switched from fail to pass.

Last edited by thom4782; 01-30-2013 at 12:33 PM.
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Old 01-30-2013, 12:37 PM   #3
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Two of the specific diagnostics steps in the decision tree for P0430 are to check the EVAP canister purge valve and the line connecting the EVAP canister purge valve and in intake system, as a problem with either will throw off the TWC conversion on bank 4-6. As you are showing a “fail” for the fuel tank ventilation system, which is the EVAP system, I’d start looking there.
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Old 01-31-2013, 04:38 AM   #4
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thom4782, The Durametric readings were taken only after about 20 miles of driving after the P0430 error code was cleared. I plan on driving the car a few more days and will check Ready Status readings again.

JFP in PA, Would it be possible for you to send me the diagnostic steps in the decision tree for the P0430 code? I believe there are some 'tests' in the Durametric program for the EVAP canister purge. I will have to take another look at that.
Any other suggestions?

Thanks
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Old 05-05-2020, 05:48 PM   #5
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What is O2 sensor resistance supposed to be?

Quote:
Originally Posted by BoxsterSenior View Post
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.
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Old 05-06-2020, 07:42 AM   #6
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OK, let try and clear this up: If the cats were working correctly, the O2 sensor ahead of the three way cat should be cycling on a sine wave like curve when the voltage is traced on a scope, while the sensor behind the cat should be drawing a nearly flat voltage trace line. When they are both cycling, it means the cat in between them is dead and unable to alter the exhaust gas to meet target.

As you are getting P0420 and 0430, it indicates that both your cats are dead (the OBD II manual for the car states it as "TWC conversion rate is too low").

If you are consistently "belching smoke" on start up, the oil has done in your cats. You need to find the source of that and fix it as just replacing these very expensive cats will not help you, the new ones will just die like the original ones did.

Good luck.

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