Playin the P0421/P0431 game again + misfires
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  1. #1
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    Playin the P0421/P0431 game again + misfires

    '01 GLX V6 5spd ATQ 160k

    P03xx
    P0431
    P0421

    I have read numerous post related to these two codes, have had them both show up intermittently over the last two years, I am also getting some random misfires on all cylinders, some history -

    I have had the 'ECU reflash' procedure, I had all four O2 sensors replaced(3 oem & 1 donor) and both CATs swapped from a donor car w 60k, I have replaced the coils( whole OEM part), Plug wires(OEM), and Plugs. I have replaced the air intake filter, fuel filter, Cleaned MAF + Throttle body, replaced Vac lines, EGR purge valve, EGR plastic tubing. I pretty sure SAIP is working properly.

    Car runs fine(go figure), I use only 93, my daily commute is short(4mi) an I am in traffic mostly so the car never gets RPMs up much, I have never run the tank dry but have gotten it very low a few times. I have run some injector cleaner through it maybe twice in last two years.

    I have heard short trips, over fill oil, run tank dry, SAIP broke, as all being 'possible' causes for symptoms I am experiencing with the CATs

    With car started and running fine,I then log in to VagCom(409.1 shareware ver) and check engine module, I get all pass on the 'readiness' with the above codes showing *but* when I hit 'clear codes' it clears but then when I check readiness again it show most systems as 'fail' and car will start to misfire alittle?? <-- could VAGCom itself be causing something?

    The CEL will stay off for varying amounts of time before popping back up, weird thing is I always get BOTH P0421 and P0431 every time at the same time. occasionally the other P03xx's will show up as well, never get any other codes than these, WTH??

    Any suggestions on what else could I check or do about the misfires?
    and the 'Cat below efficiency - intermittent' P0431/P0421 codes before replacing CATs (again)?

    Oh yeh car ran fine before and after all above parts were replaced, no difference that I could tell, lol.

    Thanks Peeps,
    I love this car but DAM

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  3. #2
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    i just gave up on my p0421. now i roll with my check engine light all the time.

    it's annoying to me, but at least vw's engine light is somewhat subtle and not a big red font CHECK ENGINE. passengers never say "hey dude stop the car your engine light is on!!"

  4. #3
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    True that, however I am inclined to think that this is an indication that something else is 'out of spec' causing the codes.

    I just returned from a 25 mile trip in 3rd @5000rpm the whole time, 6 oz's of sea foam in half tank of gas, a little 'Italian Tune Up' action.
    Car ran great and smooth, codes haven't shown back up yet since last reset, but Im still failing readiness on SAIP, O2, and CATs, all else passes. Still getting random misfires while VagCom is running/hooked up??<-- could COM port settings be affecting something?

    Maybe I need to find someone locally with Full VAgCom and do some logging....

  5. #4
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    OK, in absence of another VagCom to see if my cable/shareware are causing ills, I have done some follow up on the P0421/P0431 codes.

    After reading more about the SAIP system I am trying to diagnose whether it is working properly or not. I WAS getting the loud whirring noise off and on which is usually a tell tale sign SAIP pump is going out.....I no longer get that loud noise. I pulled the relay in the box where the ECU sits and it looks mint. on Cold start I can feel the SAIP pump vibrating/running and I notice the plastic flex hose gets warm to the touch but not HOT, is this normal?

    how else can I be sure this system is functioning properly?

  6. #5
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    SAIP sounds normal. I am fighting the P0431 and P0421 codes too. I have new O2 sensors but have not had the software update. I might just add anti-foulers to the rear O2 sensors for a cheap fix.

    It's possible your 60K cats were not in good shape to start with. With as much oil as the V6 burns, I expect a lot of cat failures.

  7. #6
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    I have a 2003 Passat 2.8L with 122000 miles, got the CEL light and I looked up the code at Autozone it turns out to be P0421. Took it to the stealership and as expected I was told I would need a new right side catalytic converter which would cost approximately 1400$, I didn't want to spend that money since my emissions are not due for another 8 months, but since I was out there and was due for an Oil change, I got that done.
    The CEL light was on on my drive back home and when I parked my car. Later that evening I needed to run an errand and drove the car and it I did not see the CEL light on. Since then I have driven 200 miles plus without CEL coming back on.
    It would seem like there is some connection between the oil change and the CEL light turning off, but I am not sure what it is.
    Figured I would share it with folks here and may be someone might be able to help me understand it? Any input is appreciated. Thanks!!

  8. #7
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    Older V6 Passats like mine get the 0421/0431 codes due to a software glitch - not sure if it would explain your situation. I wouldn't pay $1,400 to anyone for a new cat - that is for sure. When both the 0421 and 0431 codes showed up at the same time, I figured it was too much of a coincidence and it's the software so I just drive it that way. Stealer won't just do a reflash w/o paying them to do a complete diagnostic check so I live with it.

  9. #8
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    I wonder if there was some leak around the drain plug or filter washer/sealant that caused the rich/air fuel mixture that got fixed the next time I got an oil change done, haven't seen the light come up yet almost 400 miles since it reset itself

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