P0422 code after replacing the cat converter and fuel system - Kia Forum
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#1 (permalink) Old 08-17-2010, 08:44 PM
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Default P0422 code after replacing the cat converter and fuel system

A month and a half ago I replaced the cat converter on my 2000 Sephia after having cleaned/replaced the entire fuel system. It solved the problem with acceleration, but the engine still idles a little rough and now, 1200 miles later, the P0422 code came on again. What baffles me is that there are no codes for misfires and I've replaced the O2 sensor recently as well. I figured that the original cat converter died because of massive fuel system problems (which I fixed), but if this one is dying, there must be another big problem which is probably causing the rough idle too. I'm at a loss as too what could cause this...how could my engine be burning rich without setting the misfire codes? Is it possible that the spark plugs are bad?
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#2 (permalink) Old 08-19-2010, 06:14 AM
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A month and a half ago I replaced the cat converter on my 2000 Sephia after having cleaned/replaced the entire fuel system. It solved the problem with acceleration, but the engine still idles a little rough and now, 1200 miles later, the P0422 code came on again. What baffles me is that there are no codes for misfires and I've replaced the O2 sensor recently as well. I figured that the original cat converter died because of massive fuel system problems (which I fixed), but if this one is dying, there must be another big problem which is probably causing the rough idle too. I'm at a loss as too what could cause this...how could my engine be burning rich without setting the misfire codes? Is it possible that the spark plugs are bad?
Im betting your gas mileage is suffering now also, correct? And Ill bet its and o2 sensor.
What o2 did you replace? There are 2. The front sensor is used by the ecu to read if fuel mixture is lean or rich and to make needed adjustments (rear is used only for the cat efficiency measure)
Youll need to replace the faulty one.

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#3 (permalink) Old 08-19-2010, 11:04 AM
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Thanks for the reply. I think the mileage is suffering a little, and I did replace the front O2 sensor (I'm assuming the front means the one closest to the engine on the exhaust line?). How do I check the rear sensor? And if it is bad, is it actually harming the cat converter or is it just a useless warning signal? And, if I did replace it and it wasn't the problem, how would I know that the problem isn't solved? Would the P0422 code come back on?
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#4 (permalink) Old 08-19-2010, 11:09 AM
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Oh, and why would the P0422 code (dealing with the bank 1 sensor) show up instead of the P0432 which deals with the bank 2 sensor?
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#5 (permalink) Old 08-20-2010, 08:49 AM
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Oh, and why would the P0422 code (dealing with the bank 1 sensor) show up instead of the P0432 which deals with the bank 2 sensor?

Hmm, I wonder if the pre cat (warm up car) is working properly. Also did you fully reset the ecu after the o2 change. Or did you simply remove the neg. cable?

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#6 (permalink) Old 08-20-2010, 09:08 AM
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Yeah, I definitely had both the positive and negative unplugged from the battery for several days. What/where's the pre-cat? Wouldn't it have a obd II code?
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#7 (permalink) Old 08-20-2010, 12:38 PM
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Yeah, I definitely had both the positive and negative unplugged from the battery for several days. What/where's the pre-cat? Wouldn't it have a obd II code?
The pre-cat is the one right after the exhaust manifold. it just might throw this code, if not flowing correctly. Not positive.
Not sure but, do you have a header installed? Was it a pre-wired- plug & play o2 sensor or aftermarket? Its a what, 3 wire Been a while since I seen a sephia. Did you get the wires correct if this is the case?

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#8 (permalink) Old 08-20-2010, 02:24 PM
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No, I don't have a header or aftermarket O2 sensor.

So I figured I'd think it through a little, so bear with this logic please, and let me know if I missed something. Thanks.

What I gather is that if a catalytic converter is plugged, then I get a bad backpressure going back to the engine. I'm guessing the restricted airflow keeps the exhaust relatively rich and the first O2 sensor senses that and triggers the code.

If that's what's going on, then I might have had a bad cat converter AND a bad pre-cat. Having replacing the bad cat converter the car probably works okay now because it isn't bothered by two compounding back-pressures, but just the one from the pre-cat. If that is the case, then the main cat isn't really doing much work since everything is getting clogged upstream by the pre-cat.

So, theoretically I could test this by checking back-pressure between the two cats, or by taking off the downstream cat and looking to see if it is clean.

I guess the other possibility is that the sensor is bad, but that doesn't make sense because nothing should have been there to make it go bad. I had replaced it, but I don't think the original actually was bad (I tested it outside the vehicle with a blowtorch and voltmeter). Maybe if I switch the two and the code doesn't come up then problem solved, or if the code does come up then the problem isn't the O2 sensor.

Also, I don't see how the bank 2 sensor could be the problem in either scenario...
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#9 (permalink) Old 08-20-2010, 03:34 PM
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No, I don't have a header or aftermarket O2 sensor.

So I figured I'd think it through a little, so bear with this logic please, and let me know if I missed something. Thanks.

What I gather is that if a catalytic converter is plugged, then I get a bad backpressure going back to the engine. I'm guessing the restricted airflow keeps the exhaust relatively rich and the first O2 sensor senses that and triggers the code.

If that's what's going on, then I might have had a bad cat converter AND a bad pre-cat. Having replacing the bad cat converter the car probably works okay now because it isn't bothered by two compounding back-pressures, but just the one from the pre-cat. If that is the case, then the main cat isn't really doing much work since everything is getting clogged upstream by the pre-cat.

So, theoretically I could test this by checking back-pressure between the two cats, or by taking off the downstream cat and looking to see if it is clean.

I guess the other possibility is that the sensor is bad, but that doesn't make sense because nothing should have been there to make it go bad. I had replaced it, but I don't think the original actually was bad (I tested it outside the vehicle with a blowtorch and voltmeter). Maybe if I switch the two and the code doesn't come up then problem solved, or if the code does come up then the problem isn't the O2 sensor.

Also, I don't see how the bank 2 sensor could be the problem in either scenario...
Well bank 2 is for cat efficiency. So if the catalyst system is not working properly you might get this code. Maybe?
I'd check the cats, thats what I think.
Or is the manifold, or either cat have a good sized leak?
and a good start on the o2's would be looks. Really black or white? Its common to be whitish though from my experience with the 1.8.
Somethings wrong with the combustion if the sensors check out and cats. What else controls the air/fuel mixture?

Maybe clean the maf sensor. If its dirty you could get a bad mix. And with its input to the ecu, it works directly with the o2.

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Last edited by 1fastkia; 08-20-2010 at 03:42 PM.
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#10 (permalink) Old 08-20-2010, 05:18 PM
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Alright, I guess it's time to get my hands dirty again
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