P0431 P0421 codes

  1. Welcome to VW Passat Forums : Volkswagen Passat Forum – General discussion forum for Volkswagen Passat

    Welcome to VW Passat Forums : Volkswagen Passat Forum - a website dedicated to all things Volkswagen Passat.

    You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, Join VW Passat Forums : Volkswagen Passat Forum today!
     
Results 1 to 9 of 9
Like Tree6Likes
  • 1 Post By Emry
  • 1 Post By PZ
  • 1 Post By Btitans
  • 3 Post By RCinSTP

Thread: P0431 P0421 codes

  1. #1
    1st Gear
    Join Date
    Aug 2010
    Location
    Saint Paul, MN
    Posts
    314

    P0431 P0421 codes

    I'm getting codes

    P0431 Warm Up Catalyst Bank 1 Efficiency Below Threshold

    P0421 Warm Up Catalyst Bank 2 Efficiency Below Threshold

    where do start for diagnosing? It looks like both driver and passenger side, but, do these codes relate to Upstream (before the Catalytic Converter?) or Downstream (after the cat)?

    Is there a way to test the O2 sensors, because if the sensor is bad, I will replace it, if the sensor is good, I will add a spacer. Would O2 sensors on both sides go bad at the same time?

  2. Remove Advertisements
    VW Passat Forum
    Advertisements
     

  3. #2
    in dire need of an organic chemistry lesson
    Join Date
    Jul 2007
    Location
    Michigan
    Age
    56
    Posts
    2,172
    Quote Originally Posted by RCinSTP View Post
    Is there a way to test the O2 sensors
    Do you have a scanner to read the live O2 sensor values?

    Quote Originally Posted by RCinSTP View Post
    Would O2 sensors on both sides go bad at the same time?
    Very unlikely that both go bad at the same time. Nevertheless, that is not the issue here. Just get the values and see if they indeed gone bad.
    RCinSTP likes this.

  4. #3
    PZ
    PZ is offline
    Redline
    Join Date
    May 2002
    Location
    Grapevine TX. 01 4M
    Age
    56
    Posts
    25,839
    These are for the downstream sensors. It could be bad flex pipes as that allows air into the exhaust.

    If the flex pipes are good, just add spacers to the rear O2 sensors. On earlier V6 engines, there was a software update as the parameters were (supposedly) set too low.
    RCinSTP likes this.

  5. Remove Advertisements
    VW Passat Forum
    Advertisements
     

  6. #4
    Neutral
    Join Date
    Feb 2019
    Location
    Vermont
    Posts
    124
    age/mileage?
    o2 sensors ever been replaced?
    cats ever been replaced?

    I thought you got the 2096 and whatever the other side error is when you have flex pipe hole issues...4031/4021 usually was 02 sensors.

  7. #5
    1st Gear
    Join Date
    Aug 2010
    Location
    Saint Paul, MN
    Posts
    314
    I don't have have access to the car right now, but as soon as I do, I will check things and reply back. I just happen to have some spacers so I might start with adding spacers and then check the VCDS Vag-Com software again. The flex pipes are a bit worn but still solid and seem to be sealed tight.

  8. #6
    Neutral
    Join Date
    Apr 2011
    Location
    NY
    Posts
    18
    Leaks most likely at the flex joints. You can start it cold and run your hand around joints, you should feel something before it gets too warm to touch.
    RCinSTP likes this.

  9. #7
    1st Gear
    Join Date
    Aug 2010
    Location
    Saint Paul, MN
    Posts
    314
    Thanks, Btitans, I appreciate the tips about the flex pipes. I wanted to know how they could be checked for leaks.

    Thanks, Emry, PZ and ar393, I didn't realize how much could be checked with the VCDS (VAG-COM) software, I generally just use it to look for fault codes.

    I turns out that the Fault codes were caused be one of the cylinders misfiring. I completely forgot that I couple of months ago, this same car (my wife's car), had the #2 cylinder spark plug wire go bad. I checked the software and just like last time, one of the cylinders was misfiring a lot. I replaced that plug wire (the wire that runs from the coil pack at the front of the V6 engine, to the spark plug), and the car has been running great since then, no mis-fires.

    I plan to buy a set of high-quality plug wires and replace all the wires.

    Thanks again for your help and advice.
    cchief22, PZ and Emry like this.

  10. #8
    Neutral
    Join Date
    Feb 2019
    Location
    Vermont
    Posts
    124
    Quote Originally Posted by RCinSTP View Post
    I turns out that the Fault codes were caused be one of the cylinders misfiring. I completely forgot that I couple of months ago, this same car (my wife's car), had the #2 cylinder spark plug wire go bad. I checked the software and just like last time, one of the cylinders was misfiring a lot. I replaced that plug wire (the wire that runs from the coil pack at the front of the V6 engine, to the spark plug), and the car has been running great since then, no mis-fires.

    I plan to buy a set of high-quality plug wires and replace all the wires.
    Hehe, I need replace my #2 Cylinder wire now myself. At some point down the line I may get some higher end wires.

  11. #9
    3rd Gear
    Join Date
    Jul 2013
    Location
    Chagrin Falls,Ohio
    Posts
    1,181
    have to chuckle......it's like my car is reading/listening to these posts, I'll read something about .............vacuum leaks and misfires as an example..... and on the way home I get misfires/vacuum leaks......,however glad you got 'er solved

  12. Remove Advertisements
    VW Passat Forum
    Advertisements
     

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Where do you live?

Year of model

car model

Please select your insurance company (Optional)

Log-in

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

    Tags for this Thread

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •  
    Powered by vBadvanced CMPS v4.1.2