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Service indicator and how does it work?

Discussion in 'Engine' started by merovingian, Dec 13, 2016.

  1. merovingian

    merovingian New Member

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    Can anyone explain the criteria for my c220 cdi 2005 service indicator?
    Just had a reminder to do a service B which i passed by a couple of weeks. I work at home and the car has done maybe 2500 kms in the last year. I usually take my motorhome if I go anywhere distant.

    How does the ECU know if a service is due, by time and or mileage obviously, or is it feindishly more clever; or is that entirely reserved for the most recent models?
     
  2. markjay

    markjay Hardcore MB Enthusiast

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    The relevant input also includes number of engine starts, engine revs and temp, and oil and filter type.

    But ultimately the system does not actually check the oil quality as such - it simply makes an a assessment based on usage history.
     
    Last edited: Dec 13, 2016
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  3. whitenemesis

    whitenemesis Hardcore MB Enthusiast

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    The car checks the oil quality by measuring the conductance. Conductance goes up the more the oil degrades or gets contaminated. This and the above mentioned usage history goes towards determining service intervals. Oh, and by the number of days since the last service.
     
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  4. Rory

    Rory Hardcore MB Enthusiast

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    The more recent models are on fixed interval (12 months or 15,500 miles) servicing. MB moved to that around 2007.

    Yours could have been set for fixed interval (my dealer kindly offered to do that on mine :rolleyes: ) hence it's come up after a year.

    As to how the variable bit works, it's been discussed many times and I don't think anyone (outside of Mercedes) really knows. I do about 6000 miles per year, but that's mainly one long round trip per month - day-to-day I don't use the car. For the last few services mine has run to the full 2yrs (which is the maximum).

    One thing (for extended interval servicing) is the oil quality has to be set correctly and then you get a 1.3 multiplier on the mileage. So at reset mine shows 13000 miles to service, but whenused for long journeys it counts down 100 miles for every 150 the car does. So the max possible mileage would be 19,500.
     
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  5. OP
    OP
    merovingian

    merovingian New Member

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    Interesting and indeed fiendishly clever. I will have a look at the date of the last oil change and based on that draw my conclusions as to wether its simply annual or its due to starts and stops or "conductance" which I can only liken to resistance measured in Ohms
     
  6. markjay

    markjay Hardcore MB Enthusiast

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    1. Some models are fitted with 'oil quality sensor' which measures conductivity.

    2. Up to MY 2007, the service interval was flexible, and on low annual mileage cars you can expect to see service intervals of between 15 and 24 months. From MY 2007 onwards, the service interval is fixed at 12 months (unless required earlier due to annual mileage)
     
  7. such01

    such01 Hardcore MB Enthusiast

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    My service indicator has gone from service in 11500 miles to service in 190 days B7

    Why the change?

    Thanks
     
  8. Bobby Dazzler

    Bobby Dazzler Hardcore MB Enthusiast

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    Are you doing very low mileage?

    With 11500 miles to go in the next 6 months, compared to say 2500 miles in the last 6 months, perhaps the car decided you'll be limited by time and not mileage, so days will be a better indicator for you. Just a guess mind.
     
  9. markjay

    markjay Hardcore MB Enthusiast

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    This is correct. When the mileage between services is very low, the car switches from mileage-based service interval to time-based service interval.
     
  10. DrNick

    DrNick Hardcore MB Enthusiast

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    I'd be surprised if it measures conductivity. Our tests showed that to be a rubbish way of doing it. You are better off measuring the dielectric properties but even then you need to start with a very well behaved oil that is well characterised. Normally this means buying a special oil from the manufacturers.
    I havn't looked at it for a while so I'd be interested if anybody has any newer information on oil quality sensing and if its actually done in any meaningful way.
    My rather cynical view is that when this was being pushed the conclusion people came to was that in most cases oil was lasting longer than they expected, resulting in less visits to the service centre, with a resulting loss of revenue. Things then switched back to a time based limit which conveniently is now annual. I don't believe there is any evidence to say that oil wears out after a year if you do low mileage! Thus I conclude there is a commercial imperative at work here.
     
  11. DrFeelgood

    DrFeelgood Hardcore MB Enthusiast

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    Don't they simply alert every one or two years or at a set mileage whichever comes first?
     
  12. whitenemesis

    whitenemesis Hardcore MB Enthusiast

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    Certainly the 219 from 2005 measures oil conductance, as documented in WIS. I'm sure other models do to. One can extend the service interval significantly just by topping up with fresh oil.

    As has already been stated current trend is pure time based intervals.
     
  13. DrNick

    DrNick Hardcore MB Enthusiast

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    This is the traditional way of doing it.
    However, two minutes thought will tell you that its rather arbitrary. So engineers decided to try and actually measure when the oil needs changing. After all, you wouldn't consider changing other things like brake pads on an arbitrary whim such as every year! No, you'd try to figure out a way of telling you when they need changing, such as a pad wear sensor.
    It turns out that oil is a tricky thing to measure the quality of as there are so many variables.
    It also turns out that oil quality has improved tremendously over the last few years as research has progressed into what it actually does, as has the tolerance of engine manufacture. This has resulted in oils overperforming, and so a normal service life can be pushed out a long way. Bizarrely this has made the need for a quality sensor actually more important to catch the outlier cases, and to help you wring the maximum life out of the oil.
    This is fine for commercial vehicles/ships etc where downtime is expensive, and an oil change can use 100s of litres of oil. Sensors exist for these situations though.
    Cars are different. They don't normally have a life anywhere near a commercial vehicle so in 95% of cases oil quality isn't going to be the limiting factor. This makes it more of a marketing issue. If you offer a super high tech variable service interval, you can use that to sell more cars.
    However, you then sell less oil at services because there are less services if it works properly. Thus there would appear to be a compromise whereby you offer some form of high techery but hobble it so the cars still come back for near annual services.
    Companies seem to have got bored with that so have now moved back in general to annual services (Oil is only one thing that needs maintenance after all!) with the option to either buy a discounted service plan, or by buying several years servicing in advance to keep you coming back
     
  14. markjay

    markjay Hardcore MB Enthusiast

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    1. According to MB, the oil quality sensor measured electrical conductivity of the oil inside the sensor's chamber. However, not all models are fitted with this sensor, and MB do not say if the oil quality sensor is one of the input factors for the flexible servicing regime. It is not impossible that it simply alerts the driver when the oil has too much water in it - or ferrous particles - I don't know.

    2. The reason that MB switched to fixed annual service in 2007 was to make their vehicles more attractive to fleet managers. When the flexible servicing regime was first introduced it was thought that the reduced overall cost would appeal to fleet managers, but this turned out not to be the case - fleet operators were more concerned about the inability to predict, schedule, and manage service schedules. This is again officially according to MB - whether there were more sinister intentions behind this, I do not know.
     
    Last edited: Dec 14, 2016
  15. DrNick

    DrNick Hardcore MB Enthusiast

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    There seems to be conflicting opinion

    Mr Whitenemesis in the past has quoted the WIS which says it uses capacitance


    Extract from WIS doc #gf1840p411102am

    "The oil sensor operates in accordance with the capacitive
    measuring principle and features integrated electronics which
    analyze the three signals (oil level, temperature and quality).

    Oil level and oil quality are detected on the basis of the capacitance of the engine oil (dielectric).
    The capacitance of the engine oil is as much as 6 times greater if the oil quality is poor."

    Maybe they have used more than 1 type of sensor. It seems to have started a heated forum discussion in the past!
     
  16. Yugguy

    Yugguy Hardcore MB Enthusiast

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    I don't believe my 58 c220 does any form of oil condition check as I did a midterm oil change and it made no difference to the service due date.
     
  17. DrFeelgood

    DrFeelgood Hardcore MB Enthusiast

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    That's the problem with over thinking.
     
  18. whitenemesis

    whitenemesis Hardcore MB Enthusiast

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    Was that date 1 yr from the last service?
     
  19. OP
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    merovingian

    merovingian New Member

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    Well I seem to have gone 18 months between oil changes, I last changed in April 2015 after 6000 kms
     
  20. OP
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    merovingian

    merovingian New Member

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    Trust the CPU

    So Can I trust the CPU to tell me when to change oil or not or should I err on the side of caution and change annually for low mileage?
     

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