fault code p0420

  1. Established Member Joined: Feb 2010 cardiff Posts: 1414 saxo Vtr
    #1
    does any one know what it means when i looked it up it came back with catalyst efficiency threshold (bank1) i also looked deeper and it could be temp sensor..cat..o2 sensor
  2. Saxperience Post Whore Joined: Jan 2008 ..... Posts: 5231 ..............
    #2
    Car year? what is it? and single plug or 3 plug ecu? ( can help diagnose what it is more)


    code P0420 may mean that one or more of the following has happened:

    * Leaded fuel was used where unleaded was called for
    * An oxygen sensor is not reading (functioning) properly
    * The engine coolant
    temperature sensor is not working properly
    * Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
    * Retarded spark timing
    * The oxygen sensors in front and behind the converter are reporting too similar of readings
  3. Established Member Joined: Feb 2010 cardiff Posts: 1414 saxo Vtr
    #3
    yes i know so it could be many problems but i dont what to go buying all sorts to fix 1 problem
    vtr 2002 3 plug
  4. Saxperience Post Whore Joined: Jan 2008 ..... Posts: 5231 ..............
    #4
    Get underneath, move the cat side to side? does it rattle?

    check for exhaust leaks.

    The sensor after the cat could be faulty or the cat faulty which makes the lambda sensor after the cat read wrong.

    Try a second hand lambda(after cat) around tenner..

    if not, then new cat. Second hand they aint that dear - 30? i remember seeing one brand new for 50- not sure on its quality mind
  5. Established Member Joined: Feb 2010 cardiff Posts: 1414 saxo Vtr
    #5
    cat dont move ..no leaks.. i see if i can get another sensor but it the 1 after the cat ??
    thanks for your info
  6. Frequent Poster Joined: Jun 2006 Cheshire Posts: 621 mk2 Icelandic Vts.
    #6
    If you have got a decat on mate this code will come on mine does it all the time
  7. Regular Poster Joined: Oct 2008 Gateshead Posts: 429 Icelandic MK2 VTR
    #7
    I get this code on mine also. Got 2 New sensors in an 1 year old cat. Came up after I got rid of the de cat pipe. Puzzles me also.

    Sent from my HTC Desire S using Tapatalk
  8. Saxperience Hardcore! Joined: Dec 2007 smurfland. Posts: 17346 Ex saxo owner.
    #8
    Quote:
    Originally Posted by huricane View Post
    cat dont move ..no leaks.. i see if i can get another sensor but it the 1 after the cat ??
    thanks for your info
    The 2nd lambda sensor doesn`t really do a lot,most probs seem to be from the 1st one.

    Edit: just looked in my haynes fault code manual & po420 is listed as catalytic convertor below threshold effeciency.