VW Beetle 2004 model

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  • David Green
    Senior Member
    • Oct 2009
    • 382

    VW Beetle 2004 model

    At the moment we have a Bettle in with the Check Engine Lamp On. I carried out an mot test on it and didn't notice any lights on in the instrument display, and it did pass the emissions test.

    The car was then serviced by one of my colleagues before the car left us. The following day the car arrives back with the lamp on. My boss puts his Snap On scanner on it and diagnosis Lambda Sensors faulty?

    So they are changed and the lamp is still present, the fault still exists?

    Today he asks me to have a look at lambda sensor 2, he says that this sensor is 'open circuit' and stopping the front lambda sensor from switching?

    I checked live data on the scanner and the lambda sensor 2 voltage was reading up to 0.40 Volts.

    The front lambda sensor reading with regards to the Snap On scanner live data reading does not exactly make it clear that it is reading the voltage?

    The reading shows 0.998 - 1000, mostly reading 0.998, but no symbol 'V' to indicate whether it is reading voltage or a ratio?

    Anyway I was not convinced that the lambda sensors were faulty and I advised my boss that I was not convinced they were. The front lambda sensor 1 before the cat reading 0.998 - 1000 to me does not look as though it is switching correctly, but when I checked the graph view the lambda looked to be switching, this was very confusing?

    I noticed also in live data that a misfire count of 02 was present. I looked on the graphs and a misfire count of 05 was present, were cylinders 01 and 03 were behaving abnormally although you could not audible hear a misfire.

    This is wear we are up to, I think may be the wrong type spark plugs fitted, but does anyone know of any other faults that may cause this condition?

    David
  • Crusty
    Senior Member
    • Dec 2007
    • 2450

    #2
    Originally posted by David Green
    At the moment we have a Bettle in with the Check Engine Lamp On. I carried out an mot test on it and didn't notice any lights on in the instrument display, and it did pass the emissions test.

    The car was then serviced by one of my colleagues before the car left us. The following day the car arrives back with the lamp on. My boss puts his Snap On scanner on it and diagnosis Lambda Sensors faulty?

    So they are changed and the lamp is still present, the fault still exists?

    Today he asks me to have a look at lambda sensor 2, he says that this sensor is 'open circuit' and stopping the front lambda sensor from switching?

    I checked live data on the scanner and the lambda sensor 2 voltage was reading up to 0.40 Volts.

    The front lambda sensor reading with regards to the Snap On scanner live data reading does not exactly make it clear that it is reading the voltage?

    The reading shows 0.998 - 1000, mostly reading 0.998, but no symbol 'V' to indicate whether it is reading voltage or a ratio?

    Anyway I was not convinced that the lambda sensors were faulty and I advised my boss that I was not convinced they were. The front lambda sensor 1 before the cat reading 0.998 - 1000 to me does not look as though it is switching correctly, but when I checked the graph view the lambda looked to be switching, this was very confusing?

    I noticed also in live data that a misfire count of 02 was present. I looked on the graphs and a misfire count of 05 was present, were cylinders 01 and 03 were behaving abnormally although you could not audible hear a misfire.

    This is wear we are up to, I think may be the wrong type spark plugs fitted, but does anyone know of any other faults that may cause this condition?

    David
    David, the front oxygen sensor may be what is often called a "wide band" sensor that usually has 5 wires to it. They don't cycle and switch down to 100-mv and up to 900-mv the way a normal oxygen sensor cycles. They have a normal sensor inside them but they also have a "pump cell' that uses the normal internal sensor and it puts out a VERY SMALL current to the PCM
    They're often refferred to as a "Lambda" sensor 'cause Lambda of 1.00 is actually 14.7/1 Air fuel ratio. If it is this type of sensor, they'll also be called an AF sensor (Air-Fuel)
    They do change from 1.00 but when it's up to 1.20 it is LEAN and when it goes down to .95 it is RICH (opposite to what we're used to seeing). It has a much finer and quicker control of the air fuel ratio but they usually only use these as the front O2 sensor, then a normal O2 sensor behind the cat. The post-cat normal O2 sensor may have 4 wires because it usually has a heater (2-wires) and a sensor signal and sensor return/ground (the other 2-wires). Because it's after the Cat it won't (or shouldn't) switch if the Cat is working properly.
    Toyotas and Hondas have been using these since around 2003 or 2004. Others use them now too. I suspect VW may be using this sensor combination of AF sensor in the front and a normal O2 behind the Cat.
    Google WIDE BAND and AFR sensors.
    The 2 or 3 or 4 misfires are not surprising. If it keeps climbing it'll need attention. If the misfires are 5 PERCENT then it warrants looking into at least.
    HTH

    Comment

    • David Green
      Senior Member
      • Oct 2009
      • 382

      #3
      Originally posted by Crusty
      David, the front oxygen sensor may be what is often called a "wide band" sensor that usually has 5 wires to it. They don't cycle and switch down to 100-mv and up to 900-mv the way a normal oxygen sensor cycles. They have a normal sensor inside them but they also have a "pump cell' that uses the normal internal sensor and it puts out a VERY SMALL current to the PCM
      They're often refferred to as a "Lambda" sensor 'cause Lambda of 1.00 is actually 14.7/1 Air fuel ratio. If it is this type of sensor, they'll also be called an AF sensor (Air-Fuel)
      They do change from 1.00 but when it's up to 1.20 it is LEAN and when it goes down to .95 it is RICH (opposite to what we're used to seeing). It has a much finer and quicker control of the air fuel ratio but they usually only use these as the front O2 sensor, then a normal O2 sensor behind the cat. The post-cat normal O2 sensor may have 4 wires because it usually has a heater (2-wires) and a sensor signal and sensor return/ground (the other 2-wires). Because it's after the Cat it won't (or shouldn't) switch if the Cat is working properly.
      Toyotas and Hondas have been using these since around 2003 or 2004. Others use them now too. I suspect VW may be using this sensor combination of AF sensor in the front and a normal O2 behind the Cat.
      Google WIDE BAND and AFR sensors.
      The 2 or 3 or 4 misfires are not surprising. If it keeps climbing it'll need attention. If the misfires are 5 PERCENT then it warrants looking into at least.
      HTH
      Thanks for that information Crusty, few things there I had not thought about like the Wide Band Sensor operation, yes I knew about it but not realising it on the car, except I knew something was different by the CAT Bank 1 sensor signal 0.998 - 1000 not showing the symbol 'V' like the rear sensor did?

      The Snap On Solus Pro Scanning graph data did the trick though, I saw the misfire count and the number of cylinders with the faults present Changed the plug leads (My Colleague did), the fault did not re-apear and all seems well now

      Thanks for your reply, much appreciated

      David

      Comment

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