Code PO431
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Code PO431
I have a 02 A4 and the CEL comes on with a code of PO431 (Catalytic eficiancy below treshold - Bank 2) Does this mean bad O2 sensors or bad Catalytic Converter? I've been reading online about this code and some people are saying that it's the O2 sensors and some are saying that it's the Catalytic Converter. Any suggestions?
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I have a 02 A4 and the CEL comes on with a code of PO431 (Catalytic eficiancy below treshold - Bank 2) Does this mean bad O2 sensors or bad Catalytic Converter? I've been reading online about this code and some people are saying that it's the O2 sensors and some are saying that it's the Catalytic Converter. Any suggestions?
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From: Washington
the way the system actually figures out cat efficiency makes me think o2 sensor is highly unlikely. its looking for the rear o2 sensor so have a smooth pattern without much activity, meaning the cat is doing it job. if it starts seeing too much fluctuation in correlation to what the front o2 sensors are saying, it throws a code for the offending bank. Its usually the cat itself, vw/audi seems to have made a big batch of junk ones.
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Yes, it's a 3.0. I've also noticed that the car vibrates when it's in gear. Not sure if it has anything to do with the CEL.
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AudiWorld Senior Member
Joined: Mar 2005
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the way the system actually figures out cat efficiency makes me think o2 sensor is highly unlikely. its looking for the rear o2 sensor so have a smooth pattern without much activity, meaning the cat is doing it job. if it starts seeing too much fluctuation in correlation to what the front o2 sensors are saying, it throws a code for the offending bank. Its usually the cat itself, vw/audi seems to have made a big batch of junk ones.
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If your cat is clogged, it can create misfires on the bank its on. A bad bank 2 cat will cause misfires on bank 2 of the engine and make is run rough.
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From: Washington
That's not how the system checks the cat efficiency. It changes the mixture and look at the front and rear O2 sensors readings during the test phase, not just looking at a stable rear O2 sensor. Based off the front reading changes, it will compare it to the rear readings and determine the cats efficiency, BUT, if the O2 sensors are aging and are off there specs, it can through a false cat efficiency fault. That's why the first repair to try is O2 sensors, more so on an older car.