SL500 stuck in 2nd gear

Discussion in 'Engine' started by 230K, Oct 17, 2011.

  1. 230K

    230K Hardcore MB Enthusiast

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    Hi

    My 1999 SL500 has been doing strange things, for the last year it needed turned off and restarted to reset something that kind of made it lethargic and not kickdown etc. Turning on and off usually resets it.

    Yesterday however it locked in 2nd gear and would change up or down but had full power etc.

    I got it put on STAR today and battery voltage, MAF & transmission speed sensor were the 3 faults stored.


    All codes erased and she drove for 30 mile or so until it started playing up and not its stuck in 2nd gear again.

    Sitting on STAR voltage was 12.11v with ignition on. During the hard frost last year the battery went totally flat and was only restored with a few days on a ctech charger on restore function. Also yesterday when locked in 2nd gear i took the MAF out and cleaned with isopropanol.

    Could the flat battery last year have stored the fault and also me cleaning the MAF yesterday may have stored a code.

    Question is................ What is wrong with her??

    I am getting codes read again sometime this week to see what is new.

    I was told that a poor battery can damage the speed sensor in the gearbox.

    Is it MAF, sensor in gearbox or battery.

    What do you guys think??

    230K
     
  2. Grahamcol

    Grahamcol Hardcore MB Enthusiast

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    My money would be on the gearbox speed sensor. To be honest, I'm not an expert but I've not heard of the battery causing damage to the speed sensor. That said, low voltage does cause Merc electronics to play up a bit but I believe any such problems are usually cured when the battery is either charged or replaced. My C200 autobox very occasionally goes into limp mode where the last known "good gear" is held. By switching off and restarting it goes back to normal again, sometimes for well over 12months before playing up again. I'm convinced in my case it's the gearbox speed sensor on the electro plate inside the box. Don't know whether a full star test might help. I believe it's possible to unplug the MAF to see whether this improves the situation. If it does then this would point to problems with the unit which would then likely need replacing. Good luck with it all.
     
    Last edited: Oct 18, 2011
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  3. Kingy68

    Kingy68 Hardcore MB Enthusiast

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    My fathers 2000my C220 auto started playing up in the cold weather last year. Throwing error codes up and going into limp mode. Tried allsorts as the battery was starting the car and holding a charge so battery was dismissed. In the end after months of intermittent trouble he was so fed up he had a new battery fitted and fault codes removed at same time. It solved the problem for him.
     
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  4. Alex Crow

    Alex Crow Hardcore MB Enthusiast

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    OK, we have a few issues here but I will work through the information...

    The gearbox sometimes holds a low gear until ignitiom is turned off/on;

    IF the gearbox ECU has a stored fault code for voltage supply to the solenoid valves then yes, suspect battery. However, this scenarion is most common after the first start of the day (obviously), and is unlikely to happen after 30 miles of driving. If the low voltage codes are stored in other modules but not the gearbox ECU then you have no reason to suspect the battery. The MAF sensor will not cause it to hold a low gear either, so this leaves the speed sensor fault codes as being the most likely - quite possibly it is an electroplate issue.
    You do need to verify oil level though, and really a proper diagnosis should always be done before replacing any parts.
     
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  5. BTB 500

    BTB 500 MB Club Veteran

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    I've also never heard of low voltage damaging sensors.

    Locking up indicates the gearbox has gone into 'limp home mode' (incidentally this is normally 3rd gear rather than 2nd) which can be caused by a range of things; you do need to get the current faults read to see if the MAF is still showing up.

    On mine it was the 'gearbox electrical plate' that gave this issue - IIRC the fault code was something to do with a mismatch between shaft speeds. This is a common problem with the 5 speed box and not that expensive to fix.
     
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  6. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    Update:

    After getting stuck in 2nd gear yesterday i got it plugged in today again and the only fault recorded this time was transmission rpm/speed sensor. Fault cleared and she is driving lovely at the minute 15 miles or so, but i was being gentle:)

    This means a new electric plate kit????

    230K
     
  7. BTB 500

    BTB 500 MB Club Veteran

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    Sounds like it. Cost about £300 all-in on mine, IIRC.
     
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  8. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    Hi

    I am about to order sump gasket, filter, washer for sump & T/C, pilot bush, a magnet and electric kit A1402700861 oh and 8 litres of oil.

    Anything else I should get??

    Also does that part number seem correct? There seems to be mention of A1402701161 as the electrics kit but it is £45 more expensive than the 0861 part number on the Inchape site. Anyone confirm????

    Thanks,

    230K
     
  9. BTB 500

    BTB 500 MB Club Veteran

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    Yup sounds good. Dug out the invoice for mine and parts listed were:

    A1402700861 gearbox conductor plate
    A1402710080 gasket
    A1402770095 filter
    Gearbox electrical switch & seal (no part no. shown)
    Gearbox oil

    Total for parts & labour was £371 (this was 4 years ago though).

    HTH :)
     
  10. renault12ts

    renault12ts MB Club Veteran

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    Hi 230k...saw you today...got the winter wheels on I see.
     
  11. BlackC55

    BlackC55 Authorised Forum Sponsor Authorised Forum Sponsor

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    Are you going to do it yourself?

    If you are; I can give you some tips. Done hundreds of them.
     
  12. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    I was engrossed in a conversation on the phone and only as you drove by (and the smoke cleared:eek:) i realised who it was. Winter wheels have been on all summer too:D

    230K
     
  13. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    Yes I am going to have a go at it myself so any pointers would be welcome.

    Thanks,

    230k
     
  14. renault12ts

    renault12ts MB Club Veteran

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    Yes...the smoke...good innit.:D
     
  15. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    What is going on there?? Its smoking like a Maghera spec Seat Toledo:eek::D

    230K
     
  16. OP
    OP
    230K

    230K Hardcore MB Enthusiast

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    Hi

    UPDATE:

    Today i changed the electrics plate and all is fine again, took over 8 litres of oil to refill, after the gearbox had adapted it is now shifts super smooth.

    Happy man:D

    It is not that difficult to do.

    I took loads of pics whilst i was doing it and if anyone is interested i will post a how to.

    230k
     
    Last edited: Nov 13, 2011

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