Limp mode?

Discussion in 'Engine' started by MercFanUk, Sep 22, 2008.

  1. MercFanUk

    MercFanUk Hardcore MB Enthusiast

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    hello, I have a w202 C180 (facelift), and I have a problem:

    I just installed some audio equipment, and I had to attach my amp to the battery - I did so with the small screw of the main Pos feed. All went well, however no my gearbox wont change higher than 2nd and is sooooo slow... Is this limp mode?

    I took the MAF of to see if it was that, and while it was nice and revvy again for 10 secs, it soon cut out completely... MAF is now back in ;)

    If it is limp mode, how can I fix it without having to pay for a star machine reset? I ried leaving the engine running for 10 mins, and also tried leaving the electrics only on for 10 mins aswell, both failed to get the autobox back to normal.

    Everything else is fine, and theres no warning lights at all. Please help!
     
  2. Buggerlugs

    Buggerlugs Hardcore MB Enthusiast

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    Hi Mercfan,

    Disconnecting the battery will cause a trans limp mode, so you either get it reset on a diag machine or it will eventually reset itself but it takes about a dozen hot ignition cycles, ie, start the motor and let it warm up for about 20 mins turn off and let it cool down and I mean FLAT COLD, that's one hot ignition cycle, so it might take a couple o days that way.
     
  3. OP
    OP
    MercFanUk

    MercFanUk Hardcore MB Enthusiast

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    Hi,

    I tried everything (including your suggestion - thanks by the way!), but to no avail. I took the car to an indie and discovered it needed a new MAF after all! Fitted and the car now zooms better than ever :)

    Seems me messing around with the battery was just a coincidence in the end!
     
  4. Dieselman

    Dieselman Banned

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    I was surprised to read buggerlugs battery suggestion, I've neither experienced it or heard of it.

    Anyway, pleased it's sorted.
     
  5. Buggerlugs

    Buggerlugs Hardcore MB Enthusiast

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    Hi Dieselman,

    I've seen it quite a few times, though it mainly happens when the battery voltage is low, by low, I mean around the point where the starter struggles to pull in, it also happens but less frquently on battery disconnection/reconnection. This causes one or more modules on the CAN bus to shut down or transmit implausible signals thus causing a trans failsafe as it loses critical data on the bus. You'll normally see a CAN implausible signal error code in the TCM and B+ low codes when this happens.

    I suppose I've seen it quite a lot simply because that's what I do, gearbox stuff, and I do see a lot o Mercs in limp home :(
     
  6. allias

    allias Hardcore MB Enthusiast

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    Are you sure about this? I disconnected battery today and tranny works fine but got problem with engine as it wont rev over 2500-3000 rpm. Not because of battery but because of previous problem.
     
  7. OP
    OP
    MercFanUk

    MercFanUk Hardcore MB Enthusiast

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    Limp mode causes the rev's to be kept low so as not to cause any damage to the Engine.
     
  8. allias

    allias Hardcore MB Enthusiast

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    I know that its just a case hoe to take care of it without Star equipment
     
  9. OP
    OP
    MercFanUk

    MercFanUk Hardcore MB Enthusiast

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    I'm not sure you can, I think it'll need the codes clearing with a STAR.
     
  10. Bellow

    Bellow Hardcore MB Enthusiast

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    Wierd for me, a smart owner, to be reading all the above. On a smart, limp mode and a whole host of other electronic ailments are cured by disconnecting the battery for 10 minutes. Even clears fault codes and re-educates the ECU to new tyre sizes.
    Who would have thought that the other cars of Mercedes would be the opposite?
     
  11. BlackC55

    BlackC55 Authorised Forum Sponsor Authorised Forum Sponsor

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    Really?

    The fault codes stay if you disconnect the battery on a Smart. NOTHING permanant is cured by disconecting the battery.
     
  12. Bellow

    Bellow Hardcore MB Enthusiast

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    Perhaps you can come to the dealer with me and protest on my behalf for re-reimbursement of the £285 bill I paid to get a faulty MAP sensor replaced. The dealer told me it cost that because they couldn't retrieve the fault code after me conducting battery disconnects to get it out of limp mode.
     
  13. BlackC55

    BlackC55 Authorised Forum Sponsor Authorised Forum Sponsor

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    They are telling you porkies!
     
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