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Author Topic: Fault code P0420  (Read 8078 times)

Offline khans1026

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Fault code P0420
« on: August 03, 2015, 03:21:52 pm »
Hi All,

I've searched the forum, but cannot see any resolution to my issue.

So a few weeks ago, I was running low on fuel and got a little lost after dinner - I eventually found a petrol station when I was literally on one bar of fuel.

As I approached the petrol station the engine warning light came on.

I thought it might have has something to do with the fuel running so low. So I filled Gino up and drove him home slowly.

I parked him up and left him over night, in a hope that the warning light may go off.

Next morning, started him up. I looked on other forums where some people advise disconnecting the battery which I did over night. Light still on.

A friend of mine plugged Gino into a generic handlheld reader, which for some strange reason turned the light off but no code was stored.

A few days later came back on again.

I took Gino to the Doctors (service garage near work) to get him plugged in again.

He produced a fault code P0420 - something to do with the CAT. Garage advised that the code was cleared and to go back to them if the light comes back on. Its currently off.

Any ideas on what the problem could be?

My setup - Abarth 500 SS with a turbo back exhaust system with a 200 cell sports cat.

Any advice would be great!

AbarthForum.co.uk

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    Offline 124Abarthreplica

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    Re: Fault code P0420
    « Reply #1 on: August 03, 2015, 04:07:28 pm »
    First thing to do after any modification fault is to go back to standard configuration, ie. refit the original cat.

    Offline GTMartin

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    Re: Fault code P0420
    « Reply #2 on: August 03, 2015, 04:19:41 pm »
    I did a quick Google search and the following came up as some general advice.

    Causes

    A code P0420 may mean that one or more of the following has happened:
    •Leaded fuel was used where unleaded was called for
    •A damaged or failed oxygen sensor (HO2S)
    •Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
    •The engine coolant temperature sensor is not working properly
    •Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
    •Retarded spark timing
    •The oxygen sensors in front and behind the converter are reporting too similar of readings
    •Leaking fuel injector or high fuel pressure
    •Cylinder misfire
    •Oil contamination

    Possible Solutions

    Some suggested steps for troubleshooting a P0420 error code include:
    •Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
    •Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
    •Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
    •Replace the catalytic converter

    Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

    We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

    Offline benn

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    Re: Fault code P0420
    « Reply #3 on: August 03, 2015, 09:33:48 pm »
    Ideally it needs to go on a better faut code reader not a crappy generic one.

    If its running fine though and you've cleared it see if it comes back, if it really does have a fault it will come back on quick enough.

    Offline khans1026

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    Re: Fault code P0420
    « Reply #4 on: August 04, 2015, 10:12:22 am »
    Thank you for your replies so far!

    I will wait and see if the light comes back on.

    I was charged £54.00 and am none the wiser as to what the issue is, rather frustrating.

    Also, how do you know if a garage has a “genuine or better” reader than a “generic one”.

    Thanks again!

    Offline GTMartin

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    Re: Fault code P0420
    « Reply #5 on: August 04, 2015, 10:22:27 am »
    Your Local Abarth dealer should have the correct equipment.

    Offline khans1026

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    Re: Fault code P0420
    « Reply #6 on: August 04, 2015, 11:53:18 am »
    £54 lighter with no idea what the problem is.  >:(

    Offline benn

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    Re: Fault code P0420
    « Reply #7 on: August 04, 2015, 01:45:40 pm »
    Sounds about right for most garages lol.

    Need some one with genuine dealership Fiat/Alfa tools, that would give you a specific code and narrow it right down, and you could also do live diagnostics to check things are working as they should.

    Just see if the fault code comes back, thats all you can do now its been cleared.

    Offline khans1026

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    Re: Fault code P0420
    « Reply #8 on: August 04, 2015, 02:00:06 pm »
    Thank you for the replies so far!

    Offline khans1026

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    Re: Fault code P0420
    « Reply #9 on: August 07, 2015, 01:49:09 pm »
    A quick update...

    So the light has come back on, rather frustrating.

    The garage have told me its the same code and that they can't advise what the problem is exactly apart from that its CAT related.

    They said I should look at changing the Lambda sensors, but they appear to be working fine from their checks.

    I have just put CATA Clean in the tank as this could resolves the issue.

    Apart from changing the CAT is there anything else I could do?

    Offline benn

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    Re: Fault code P0420
    « Reply #10 on: August 07, 2015, 05:51:20 pm »
    What scanner did they use, any ideas?

    Could do with getting it on a genuine dealer one or at least something like a snap on solus tool. They might give you a more specific code.

    At the moment its still a guessing game which is no good yet.

    Offline shadyracer

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    Re: Fault code P0420
    « Reply #11 on: August 08, 2015, 04:39:10 pm »
    I'd change the spark plugs too.
     Apparently the Mk2 Clio 1.2 16v often threw up fault codes pointing at faulty lambda sensor when all it needed to cure it was a new set of plugs. Unless plugs are fairly recently changed id replace them..

    Offline Bristol_Rich

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    Re: Fault code P0420
    « Reply #12 on: August 10, 2015, 07:32:26 am »
    The garage have told me its the same code and that they can't advise what the problem is exactly apart from that its CAT related....Apart from changing the CAT is there anything else I could do?

    I think you know (or choosing to ignore) the answer.... :whistle:

    First thing to do after any modification fault is to go back to standard configuration, ie. refit the original cat.

    Which means that it can then be tested against a known baseline spec/condition with a

    [...] a better faut code reader not a crappy generic one.

    which can be found at.....

    Your Local Abarth dealer [...].

    HTH


    Offline Fish

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    Re: Fault code P0420
    « Reply #13 on: August 10, 2015, 08:28:28 am »
    Might be worth trying to borrow a lambda sensor and try swapping it out for a month and see if the error makes an appearance.

    Fish

    Offline khans1026

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    Re: Fault code P0420
    « Reply #14 on: August 18, 2015, 02:36:04 pm »
    Poured CATACLEAN into the petrol tank.

    Nearly two weeks later and light is still off.