C4 depollution failure
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  1. #1
    bbg
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    Tadpole
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    Default C4 depollution failure

    Hi All,

    My 2009 C4 1.6T with 30K km has developed a "phantom depollution fail" problem. It seems common and attributed to myriad underlying failures from sensors to corroded fuse box terminals. The Citroen shop I use replaced the cam sensor in response to a fault code (no change) and considers the next likely cause to be a dodgy cam chain; I doubt that at 30K and because the car will go for 100's of k's with no worries.

    This car has no symptom excepting the fault light. It comes on soon after refueling to 50km after refueling. If the tank is kept under 2/3 full the car stays happy.

    I only use 98 and changing fuel brands and servos for a few fills has made no difference to the behaviour The owner manual has a comment

    When you are filling your fuel tank, do not persist after the third cutoff; this could cause your vehicle to malfunction.

    that suggests there is something less than robust around the tank, filler neck, cap, or pump.

    A mate suggested a new filler cap might be the fix. Any thoughts? Cheers,

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  2. #2
    Fellow Frogger
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    Default

    The tank needs a bit of room in the top of the neck to vent vapour, which is why they say not to overfill it. Applies generally.

    Possibly the chain is stretched and/or the cam timing out, but it's quite a lot of work just to check the timing.

    Direct injection engines can accumulate carbon debris on the valves and that can show up as poor performance and pollution faults. There is no fuel in the intakes to wash away deposits from recirculated gases.

    These might be worth reading through:
    The dreaded carbon build up on the intake valves...
    THP (1.6L T) Engine Inlet Decoking/Walnut Blasting

    Try the spray first as it is very much less expensive than delving into the engine. It really needs to be used at each service. The Subaru product and a few similar ones out there are fairly inexpensive options.

  3. #3
    bbg
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    Interesting. Not sure my symptom, random as it seems, is the same problem but worth my looking into. Cheers

  4. #4
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    Default

    Hi bbg
    I know nutting !! But just reading the thread for technical interest { sad case really}
    I was thinking the fault may be connected to the fuel tank fumes, and their consumption in the engine. I guess it has a carbon cannister or similar and a valve which is under computer control to suck the fumes into the manifold at some point. Would it be worth looking for details of the system so you could check it out. Inappropiate consumption of excessive fumes would show up as an oxygen sensor reading above specs perhaps, thus giving the depollution failure flag.
    Jaahn

  5. #5
    bbg
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    It does seem to have something to do with the tank from my perspective. The fault occurs immediately or soon after refueling and usually clears after a few 10's of ks. If I go back a few months the fault would come and go and come and go randomly, but more recently it has a pattern. Whatever it is seems to be slowly clearing. At one time I suspected some dirty fuel, but it has been more than long enough to clear so I will have a look at how the vapour is cleared as that seems to reflect the error. Thanks for that. Cheers,

  6. #6
    1000+ Posts dmccurtayne's Avatar
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    What fault codes are there without these it is a pointless post


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