W204 Stop/Start gradually dying.

Discussion in 'Engine' started by Colin_b, Jan 13, 2017.

  1. Colin_b

    Colin_b Hardcore MB Enthusiast

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    I've a 2012 W204 C250cdi. The start/stop function is gradually becoming slower to engage, and lasts less time.

    It occasionally turns green after a mile or so, but more usually it takes 10+ miles. The time it will operate in stop mode has gradually decreased to between 10 and 60 seconds.

    I suspect it may be the auxiliary battery on its last legs, but no errors have been flagged.

    Am I looking in the right area, or are there other things to check.

    Thanks.
     
  2. ioweddie

    ioweddie Hardcore MB Enthusiast

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    It's probably just the cold weather, more things running, heater etc mines hardly on when it's this cold and short journeys
     
  3. CabrioDave

    CabrioDave Hardcore MB Enthusiast

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    Remember that the stop-start will ONLY operate when the system is satisfied that many different things are "OK".

    These will differ on different cars, but are likely to include checks that:
    **Battery voltage is fully recovered from the initial cold start (to work again)
    **Coolant is up to working temperature (so starts will be easy, engine will be running economically, and engine wear will be reduced)
    **Car is not on a slope (car might accidentally roll, and need power steering and/or power brakes)
    **Car is completely stationary (ditto steering and brakes)
    **Internal temp and humidity are near to the required setting (so the aircon can take a rest)
    **Total electrical load is low (so the battery can handle the load for a while, while there's no input from the alternator)
    **The speed and pattern of movement doesn't indicate a "shuffling" traffic jam (so as to avoid too many consecutive starts and immediate stops)
    **The front wheels are not significantly turned (which would indicate that you are about to turn across traffic, and need the instant response when you get a gap)

    If any one of these checks fails, the engine will continue to run.

    There may be other checks - I only know of these because they are mentioned in the handbook of my Skoda (!)
     
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  4. OP
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    Colin_b

    Colin_b Hardcore MB Enthusiast

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    It is a complex system!

    It does work, just seems rather tired, as it were. I'll check the aux battery voltage and see if that looks OK.
     
  5. Headhurts

    Headhurts Hardcore MB Enthusiast

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    Mine takes ages to work properly this time of year as did my previous car (E300).

    Not too worried TBH as when weather becomes milder it will work better, not that I am a great fan of it and much prefer driving car in sport mode with Eco off and have not noticed a huge difference in MPG.


    Sent from my iPad using Tapatalk
     
  6. rorf

    rorf Hardcore MB Enthusiast

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    Stop start thing would drive me mad - auto electricians are going to have a ball down the road replacing batteries and starter motors - what a BS piece of technology:devil:
     
  7. CabrioDave

    CabrioDave Hardcore MB Enthusiast

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    It's annoying at first, and then after a while you don't notice it.

    It's all part of getting the emissions figure down - if they didn't fit that, they'd have to think of something else to save a couple of grams ... and we know how well the other things work!
     
  8. geraldrobins

    geraldrobins Hardcore MB Enthusiast

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    It seems people love it or hate it. I thinks its great and just enjoy the quietness when waiting at lights etc. I think you have to experience it before dismissing it though.
    It seems some people never like turning their engines off which annoys me slightly even when popping into a shop for a paper etc.
    It has been around for around 5 years and I have not read about any starter motors on the forums yet.
     
  9. OP
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    Colin_b

    Colin_b Hardcore MB Enthusiast

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    I eventually got round to checking the voltages. Cold, aux was 12.65v, main 11.8v. Started the car and both up to 12.8v, so that looked healthy.

    Stop/start works, but even after a 50 mile journey the stop bit only works for between 15 and 30 seconds.

    More checking, I think.
     
  10. OP
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    Colin_b

    Colin_b Hardcore MB Enthusiast

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    I forgot to follow this up at the time, so here goes.

    Lots of sensor checking, everything as it should be, no errors logged or any other symptoms at all. No loose connections or dodgy wiring in evidence.

    The randomness continues, aircon, either manual or auto operation slows it down, and it is slower to get going in cold weather.

    Though, just to irritate me, it will leap into action on a cold morning/cold engine, with aircon on full blast after 20 seconds about one start in 20.

    I have learned to live with it.:)
     
  11. ioweddie

    ioweddie Hardcore MB Enthusiast

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    Hi Colin.
    Funny since I replied earlier about temperature affecting it, My 2016 model C220d S205 is doing exactly the same as yours, no rhyme or reason as to when its actually going to work. I have a B service due on July 5th and have asked them to check the Aux battery function, and associated sensors etc.
    I will report back on here once serviced
     
  12. grober

    grober MB Club Veteran

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    Fully charged automotive batteries should measure at 12.6 volts or above. When the engine is running, this measurement should be 13.7 to 14.7 volts= alternator charge voltage ------- 11.8 v on the main battery if measured correctly seems low.
    If you are on the cars original main battery 2012-2017 = 5years old maybe time for a change?
     
    Last edited: Jun 28, 2017
  13. Wjk167

    Wjk167 New Member

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    11.8V on the main battery before you start the engine. That looks a little low. Going up to 12.8 just means the alternator is charging.

    With all the comments on the start/stop I have to say that I had it on previous cars. I used to have a '14 Insignia with start/stop. It was not a good system. Kinda worked whenever it wanted to. I changed to a '12 W204 and have never looked back. The Start-Stop is so quick and predictable. Mine is a C180 and it gets up to temp very quickly, and the SS kicks in. I do find it sometimes annoying when in "slow" moving traffic and do turn it off occasionally. Otherwise I think its a good system Mercedes have.
     
  14. jsemfa

    jsemfa New Member

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    Location of auxiliary battery

    Hi, where exactly is the auxiliary battery ? mine is c180 w205 car. Many thanks beforehand for an answer...
     
  15. markjay

    markjay MB Club Veteran

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    It is *usually* in the boot, under a black plastic cover, near the space saver spare wheel.
     
  16. ioweddie

    ioweddie Hardcore MB Enthusiast

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    Well had the B service, £437 lighter, included courtesy car insurance waiver and brake fluid change, still bloody dear for basically and oil change, at least **** Turpin wore a mask.

    With regard to the stop start, star showed no faults anywhere, they test drove it and said its probably the short journeys with air con on. Its is working but only now and then, bearing in mind its a S205 220 diesel. The 1.4 petrol Golf DSG I had on extended test drive / courtesy stop / started every time I stopped. Don't know if its diesel v petrol related
     
  17. OP
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    Colin_b

    Colin_b Hardcore MB Enthusiast

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    Same symptoms as mine. Best guess I can come up with is some of the sensors, while operating without triggering a fault, don't read consistently.

    I've checked the temp & voltage ones and they seem OK.

    At least it works sometimes. :dk:
     
  18. RonFleet

    RonFleet Hardcore MB Enthusiast

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    During the hot weather we've been enduring recently my W205's stop/start has been pretty reluctant to operate. I put it down to the car's having to drive the aircon harder.
     
  19. Haven't a clue!

    Haven't a clue! Hardcore MB Enthusiast

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    My primary concern remains that it will cause premature stress/wear of the drive chain due to multi start stress.
     
  20. ShaunB

    ShaunB Hardcore MB Enthusiast

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    I don't mind it, and it does save some fuel I suppose when stuck in traffic.
    It's slow to react I think in my wifes A200, especially at junctions

    I do have to laugh though, stop/start in an E63.
    Equally laughable is race start technology in a big E class saloon
     

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