fault code "PO431" help...

[rr444]

Hi Everyone-
I have an Audi A4 3.0 Quattro, 2003 with 96000 mi. My CEL on after a 6-hour, 350-mile drive and I had it scanned and got this code "PO431", saying: Warm Up Catalyst Efficiency Below Threshold (Bank 2)

I have no choice to drive another 350 miles home with CEL on because the dealer in new jersey quote me with $125 diagnosis and no idea what is the repair cost gonna be.

(on my way home, the mpg drops from 29 to 26. i don't know this is due to the fault code or tempature diffirence outside)

after doing some research, some people said this could be the o2 sensor went bad. it that correct? and what is the cost should i expect to fix the o2 sensor? or what other causes other than o2 sensors could be?

any responses are appreciated

[old guy]

The O2 sensors have integrated heating elements that bring them up to the proper operating temperature. Code P0431 indicates that the O2 sensor on your driver side catalytic converter is not reaching the proper operating range. The O2 sensors are usually in the $150 range online.

[rr444]

thanks a lot

[ct-esq]

The O2 sensors have integrated heating elements that bring them up to the proper operating temperature. Code P0431 indicates that the O2 sensor on your driver side catalytic converter is not reaching the proper operating range. The O2 sensors are usually in the $150 range online.

OG:

why do you think O2 sensor in this instance over Cat? I have the same issue and it is very intermittent - like 40-60 days apart.

[Dillon]

OG:

why do you think O2 sensor in this instance over Cat? I have the same issue and it is very intermittent - like 40-60 days apart.

Because the code says p0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2). If its a cat it will more likely be a p0432 or p0422 code.

Someone correct me if i am wrong.

[zz2h33]

^thats correct. if the CAT was going it should throw a 0420 or 0421.

however, the 0431 should still be considered an emissions related fault and be covered under the 80k gov't warranty.

edit: OP, sorry just read you are at 96k so your warranty is expired. next time go to autozone or the like, they will scan the code for free. never take it to the dealer with the light on not knowing what the code is, they'll get you for $125 every time. at least your cat isnt bad, because they are quite pricey to replace on the 3.0s.

[ct-esq]

Dillon and zz2h33, thanks.

Even though this wasn't my thread to start, I've got a similar issue.

To my great sadness, I'm well over 80k (about 155k now) and I'm looking at o2 sensor vs. aftermarket cat. The o2 sensor is about $150 installed and cheaper than an aftermarket cat, I'd rather have some confidence that it is the o2 sensor.

The opinions here, QW and AW are a little different on p0431. Some insist it is a cat, but many say o2.

Thanks again.

[Dillon]

The opinions here, QW and AW are a little different on p0431. Some insist it is a cat, but many say o2.

Thanks again.

Very true but honestly your best bet would be to fix the sensor before the cats considering the cats would cost alot more.. But then again its your money you may want to do sensors and cats.

[orttauq]

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however, the 0431 should still be considered an emissions related fault and be covered under the 80k gov't warranty.

Although it doesn't apply to the original poster, this wouldn't be covered under the emissions warranty.

O2 sensors failing in any which manner wouldn't be covered under emissions. Only the bumper to bumper or CPO. The catalyst is the only portion of the exhaust system covered under emissions.

Also, P0431 can mean a catalyst failure. If the sensor is good, there could either be an exhaust leak OR the catalytic converter is failing. You can't pin that code on a faulty sensor alone, and there isn't an overwhelming variance to say that it's most likely the sensor.

EDIT: Also, P0421 reads the same way. Warm up catalyst efficiency below threshold. My educated guess is that you need a new cat.

[orttauq]

(on my way home, the mpg drops from 29 to 26. i don't know this is due to the fault code or tempature diffirence outside)


any responses are appreciated

Also, you won't experience any decrease in fuel mileage from this issue UNLESS your catalytic converter is breaking up and has become extremely clogged/restrictive.

[orttauq]

Very true but honestly your best bet would be to fix the sensor before the cats considering the cats would cost alot more.. But then again its your money you may want to do sensors and cats.

Or if you take it to someone with the proper equipment the O2 sensors can be tested and you'll know.

[zz2h33]

Although it doesn't apply to the original poster, this wouldn't be covered under the emissions warranty.

O2 sensors failing in any which manner wouldn't be covered under emissions. Only the bumper to bumper or CPO. The catalyst is the only portion of the exhaust system covered under emissions.

Also, P0431 can mean a catalyst failure. If the sensor is good, there could either be an exhaust leak OR the catalytic converter is failing. You can't pin that code on a faulty sensor alone, and there isn't an overwhelming variance to say that it's most likely the sensor.

EDIT: Also, P0421 reads the same way. Warm up catalyst efficiency below threshold. My educated guess is that you need a new cat.

IDK, if you read the actual gov't 80k warranty is specifically says any component that is emissions related of which would cause the vehicle to fail emissions test, and this certainly would. however, as you pointed out this is unrelated unfortunately for the OP. if P0431 is the other bank and reads the same then i'm with you its most likely a cat.

[old guy]

OG:

why do you think O2 sensor in this instance over Cat? I have the same issue and it is very intermittent - like 40-60 days apart.

Honestly I think I gave a bad answer to the OP. More often than not the problem is the catalytic converter. You can check the heating element in the O2 sensor by unplugging the sensor (underneath the coolant reservoir) and checking the resistance across terminals 1 and 2. (terminal 1 is closest to the flat end of the harness plug). You should get a resistance reading somewhere between 1 and 20 Ohms. If you do the problem is probably the cat. If you don't then you know that the heating element is bad and the sensor needs replacing.

[orttauq]

IDK, if you read the actual gov't 80k warranty is specifically says any component that is emissions related of which would cause the vehicle to fail emissions test, and this certainly would. however, as you pointed out this is unrelated unfortunately for the OP. if P0431 is the other bank and reads the same then i'm with you its most likely a cat.

I was a VW/Audi service advisor and processed hundreds of emissions claims. Believe me, the o2 sensors are covered in no way (other than them being frozen in the catalyst piping which is being replaced under emissions warranty).

Edit: Also, a failing o2 sensor would not cause a vehicle to fail an emissions test. All it does is read whether the emissions related equipment (catalytic converter) is doing it's job. If the catalytic converter is still good, it's not going to fail an actual pipe sniffing test.

[ct-esq]

OG

thanks for the clarification. given the cost of the cats, i'm afraid i'm trying to see a cheaper fix than admit the cats are on the way out.

I can test that - 1 and 20 ohms.

BTW - i still get 23-24 mpg running 93 oct.

that being said, this CEL for p0431 follows by 48 hours, a CEL for misfire cyl 1. That misfire is on WOT, on cold start, car stumbles, etc. and flashing CEL. and this is after new plugs and 6 new coil packs.

i'm warming to the fact that it is a cat, bank 2.

is there anything else you can think correlates the 2 issues.

AND, would the "DTC Freeze" data from an OBDII scanner help you in any way with these 2 seemingly related issues?

My bet is they are related.