Question about 2000 Volvo S40

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Random check engine light on 1999 1.6 xs s40 volvo

This happend to me just bought the car??????? please help me as my engine check light comes on randomly and then i restart engine a couple of times and then goes off?

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  • willfox_17 Jul 16, 2009

    im from uk? so i will get codes for you anyway. no autozone in uk so will it be cheaper to buy a scanner or take it to volvo or just normal garage? thanks for your help

  • willfox_17 Jul 20, 2009

    These are my codes for volvo s40

  • willfox_17 Jul 21, 2009

    i can just reset them if i want i got a code reader and i can just erase the codes do you think this is wise?



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The light is indicating an emission system failure. Take the vehicle to your local Auto Zone or Advance Auto and ask them to scan your car for trouble codes, they will do it for you at no charge. Write the codes down and reply back to me and we can begin diagnosing the problem.
Good luck, let me know.

Posted on Jul 15, 2009

  • Bruce Bracey
    Bruce Bracey Jul 20, 2009

    The P0102 code refers to the Mass air flow meter located in the air inlet snorkel:

    Trouble Code: P0102
    Mass Airflow Sensor Circuit Low Input

    Possible Causes:

    MAF sensor signal circuit is shorted to ground
    ( when checking for short to ground,only the black wire should be grounded)
    MAF sensor power circuit is open (check for power from relay)
    ( Meter should indicate 5 to 12 volts on power supply)
    MAF sensor is damaged or has failed

    PCM is damaged

    The P0420 is related to the catalytic convertor:

    Trouble Code: P0420
    Catalyst Efficiency Below Normal (Bank 1)

    Possible Causes:

    Air leaks at the exhaust manifold or in the exhaust pipes

    Catalytic converter is damaged, contaminated or has failed

    Front HO2S or rear HO2S is contaminated with fuel or moisture

    Front HO2S and/or the rear HO2S is loose in the mounting hole

    Front HO2S older (aged) than the rear HO2S (HO2S is lazy)
    I believe the P0120 is causing the problem for the P0420. Once you fix the P0120 the P0420 will go away if it hasn't run too long in this condition.
    If you have access to a volt/ohm meter you can test the circuits as described for the P0120.
    Make certain the air intake snorkel hoses do not have any holes in them and that all crankcase ventilation hoses are connected. The oil cap must be sealed a locked properly. Inspect the cap seal to make sure there are no air leaks around it.
    All of these can cause the P0102 to set.
    Check them out and make sure there are no hoses cracked, missing disconnected or damaged.
    Good luck, let me know.

  • Bruce Bracey
    Bruce Bracey Jul 21, 2009

    Unfortunately, that won't fix the issue. It will clear the light until the next time it reoccurs. If the P0102 is not fixed, you run the risk of eventually ruining the catalytic converter and having to fix the P0102 anyway.

    At this point you can fix the P0102 and possibly save the converter and the added expense.

    Good luck, let me know if you wish to go further.

    Best Regards,



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