P0420: Catalyst System Efficiency Below Threshold

  1. Regular Poster Joined: Mar 2009 Lincolnshire Posts: 266 Saxo 1.4i Furio Black
    #1
    My engine management light came on about 3 weeks ago so I took the Saxo in to my local garage. The ECU had detected an error with the emissions. They said if it comes on again you probably need a new cat. Last week the EML came back on. I have just plugged my code reader into the car and the same DTC has come up again (P0420: Catalyst System Efficiency Below Threshold').

    According to http://www.obd-codes.com/p0420 this means the problem is:

    Quote:
    A 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
    Now I'm guessing it's either a new cat or lambda sensors that I need? How would I tell if it is either of these causing the problem? I would much rather do this myself than pay a garage as both the cat and sensors look relatively simple to replace (at least it looks that way in my Haynes manual ).
  2. Saxperience Forum Bum Joined: Oct 2004 Spennymoor, United Kingdom (England) Posts: 3742 Saxo MK2 VTS
    #2
    Lambda is the cheaper to replace fella.......
  3. Regular Poster Joined: Mar 2009 Lincolnshire Posts: 266 Saxo 1.4i Furio Black
    #3
    Quote:
    Originally Posted by fossie View Post
    Lambda is the cheaper to replace fella.......
    I know, but what if they're fine and it's the cat that needs replacing? Is there any way to tell without changing anything?
  4. Saxperience Forum Bum Joined: Oct 2004 Spennymoor, United Kingdom (England) Posts: 3742 Saxo MK2 VTS
    #4
    Ermmm not sure matey, the lambda you can get for around £20 - £30 like........ or take it out and give it a clean, might be carboned up
  5. Saxperience Hardcore! Joined: Oct 2005 Aycliffe Posts: 32205 Saxo VTS
    #5
    on the flip side the lambda's ability to switch between high and low reading deteriorates over time so it's good policy to change them periodically anyway.
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  6. Saxperience Hardcore! Joined: Oct 2005 Aycliffe Posts: 32205 Saxo VTS
    #6
    p.s. which code reader have you got mate?
  7. Saxperience Hardcore! Joined: May 2007 Posts: 16839 Saxo VTS, Westfield
    #7
    one way you can normally tell if the cat is buggered is, if you get underneath it and tap the cat it will rattle.
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  8. Saxperience Hardcore! Joined: Oct 2005 Aycliffe Posts: 32205 Saxo VTS
    #8
    Quote:
    Originally Posted by J222JRA View Post
    one way you can normally tell if the cat is buggered is, if you get underneath it and tap the cat it will rattle.
    meeeow surely?
  9. Saxperience Post Whore Joined: Apr 2007 Posts: 6640 Integra DC5R & VTS
    #9
    Might well just be the CAT dying tbh. If it's a 3 plug with dual lambdas, the second lambda is probably reading the nasty content in the exhaust gasses - hence telling you the CAT is dead.
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  10. Regular Poster Joined: Mar 2009 Lincolnshire Posts: 266 Saxo 1.4i Furio Black
    #10
    Quote:
    Originally Posted by adsayer View Post
    p.s. which code reader have you got mate?
    This one http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=300308740027, but mine came with a damaged software disc, so rather than wait for a new one to be posted I found some other software online which works really well. I'm using OBD-II Scanmaster software and had to download the windows drivers from http://www.ftdichip.com/Drivers/D2XX.htm.

    Here's a quick screenshot of the software in action:

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  11. Saxperience Hardcore! Joined: Oct 2005 Aycliffe Posts: 32205 Saxo VTS
    #11
    that's legendary mate... just what I need. Thanks!
  12. Infrequent Poster Joined: Feb 2009 Middlesex Posts: 106 Peugeot 106 GTi, Fiat Punto Sporting
    #12
    Scratch that.
  13. Regular Poster Joined: Nov 2008 Trowbridge (Wiltshire) Posts: 409 1986 MK1 GOLF C
    #13
    have the same sort of problem with engine management light is on and says its emmisions but could this be because i have an after market mani with a sports cat as lights been on since putting it on really cheers?

    Sorry for hijack
  14. Regular Poster Joined: Dec 2010 Posts: 369 00 VTR Saxo
    #14
    How do i diagnose these problems to see which one it is
  15. Regular Poster Joined: Sep 2011 Hertfordshire Posts: 250 2000 Saxo Woodland Green VTS, 2002 Mazda MX5
    #15
    I had the same problem on my VTR so i had an emissions test done on it at a local garage during it dreaded MOT, and from the results i diagnosed the secondary lambda was the faulty one. As im sure most of you all know your lambda should read between 0.85-1.1. I noticed the garage i took mine too only checked the pre-cat lambda reading which produced a reading of lambda 1 !

    To check the cat was working the emissions coming out were considerably below the MOT standards producing HC levels of about 20ppm and low CO2 levels (sorry can't member the true value)

    The next stage involved checking the resistance and voltage reading from the secondary lambda. From these i was able to tell this sensor was truely shagged! after replacing and switching off the ECU light, problem (so far) was solved!!!

    Although to be fair as it passed it MOT twice with the light on you could use the simple duct tape approach and cover the ECU light on the dash or unscrew the bulb! Hope this helps!!