Cruise control disengaging. 1989 300SE

Discussion in 'Engine' started by stwat, Mar 29, 2016.

  1. stwat

    stwat Hardcore MB Enthusiast

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    I've just been to stock up on important items (beer) and on a nice long stretch of road I flicked the cruise on. All was well for a mile or so but then the cruise decided to switch its self off. (Maybe it's very clever and realised I was getting close to the shop)

    Shop done and back driving the car, I try cruise again but it almost instantly disengages. It did the same a few more times till I gave up.

    Cruise control is something I have never worked on, so any tips and pointers would be gratefully received.

    Ta,
    Stu
     
  2. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    Having had a think on this, the brake light switch seems to be the logical first port of call.
     
  3. moonloops

    moonloops MB Club Veteran

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    Either that or your tyre sizes are mismatched.
     
  4. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    The tyres are all the same make and size and only a few months old.
    I havent checked the pressure in a while I must admit :eek: But would different pressures cause this issue?
     
  5. moonloops

    moonloops MB Club Veteran

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    It's the wheel speed sensors that kick cruise control out most of the time, so tyre sizes or actual faulty sensors are worth investigating along with the brake switch.
     
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  6. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    Wouldn't I get the ABS light with faulty sensors?
     
  7. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    I'd guess it would.
     
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  8. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    So that's the sensors out of the equation.

    Is there an ECU for the cruise control? Or a relay?
     
  9. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    Should have said, check out the interweb for faulty Cruise Control Amplifiers. That's what went on my W124.
     
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  10. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    Ooo I hope it ain't that. It sounds expensive, even in second hand form :eek:
     
    Last edited: Mar 30, 2016
  11. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    From what I recall it's a very common fault. Mine was cured with a used replacement amp that had been repaired and from what I understand they are very easy to repair too according to guy that fixed my C/control.
     
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  12. Stratman

    Stratman Hardcore MB Enthusiast

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    The most common fault with the CC amplifier is cracked joints, where the connector is soldered to the board. If you're in any way handy with a soldering iron it's worth resoldering all the joints and giving it another go.
     
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  13. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    Thanks gentlemen. I've repaired a few OVP's and ECU's in my time, so I'll g.I've it a go.
     
  14. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    Last edited: Mar 30, 2016
    2 people like this.
  15. gbjeppm

    gbjeppm Hardcore MB Enthusiast

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    Thats a really good find JJJ, thanks, another job I need to do at some point. Although its at the bottom of the list.
     
  16. OP
    OP
    stwat

    stwat Hardcore MB Enthusiast

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    Brilliant. Thank you:thumb:
     

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