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    vovlo s40 1.6 x reg Archived Message

    Posted by andy bates on October 13, 2008, 7:51 pm

    Hello all!
    This volvo came to me approx 3 weeks ago with EOBD lamp illuminated.Code posted PO420 (cat effeciency outside limits).After investigation it was evident that the cat had actually failed.Cat and both o2 sensors replaced - no other faults discovered.
    Vehicle has just been represented with same fault!
    After investigation the following has been noted:-
    pre - cat sensor appears to be slow switching.
    post cat sensor is switching in synchronism (not looking good for the cat !)
    co levels ok until cooling fan cuts in - initailly no change but as fan stops there is a massive increase in co (up to 4.5%),then comes rapidly down again.all voltages and relays checked ok! any suggestions?

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