1994 S500L W140 Immobiliser bypass ( sorry to ask a age old question )

Discussion in 'Electronics' started by W140s500, Jul 14, 2015.

  1. W140s500

    W140s500 Member

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    Hello and thank you to anyone who reads this and may be able to point me in the right direction.
    I have a late 1994 S500 ( UK car ) with the 1 button keyfob ( only one working ) which as it gets older, worries me more about future electrical headaches. I realise I should when I recommission the car again, which due to unreliability hasn't been used in 5 years, get another replacement remote key from MB, but have been thinking for a while it may not be such a bad thing for my personal circumstances to have the immobiliser and alarm system deactivated permanently.
    I am quite content to have the car without the factory security system and know that I never need worry about the cars anti-theft system stopping me from starting it, which it did once before when the keyfob went flat and the alarm would sound when trying to turn the key in the ignition. I will of course have a replacement security system fitted.
    The big question is I have heard of the system being deactivated, some say by the K38 relay having 2 pins connected ? Others have said cutting and joining harness wires ( does scare me a bit ) . Obviously many have had issues with this system, and I cannot justify spending a lot of money on a car which has already cost me a fortune with gremlins, and sadly isn't worth a lot of gold.
    On the positive side the car is 100% rust free, lovely body and interior, but is just cursed with electrical issues . If the immobiliser should ever shut the car down on me, then off to the breakers she shall go sadly. Any positive guidance on how to deactivate this system permanently would be greatly appreciated.
     
  2. OP
    OP
    W140s500

    W140s500 Member

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    Thank you to those who read my post; I will assume what I had hoped to do is not possible, or perhaps many would rather not post publicly how to do it. I have asked locally but no one wants to know about working on a old W140 so will leave the car in storage out of harms way !
     
  3. Dec

    Dec Hardcore MB Enthusiast

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    It might be best to get someone who knows these cars very well and it might not cost you too much to pay to have it done.
    Try this bloke here… http://alexcrowltd.co.uk/ie/

    Dec
     
  4. Parisien

    Parisien Hardcore MB Enthusiast

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    Pm me for a contact or leave an email address on this thread for another person who may be able to help

    P
     
  5. grober

    grober MB Club Veteran

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    By this time I think the alarm system is integrated into the main vehicle electronics unlike earlier cars where an aftermarket unit was piggy backed on to existing wiring. This probably means your setup is more difficult to "defeat/bypass" completely. And when you come to think about it these cars are quite complex electronically and the factory alarm system is no more likely to strand you in the back of beyond any more than one of the cars other remaining vital systems. So altho you can install a brand spanking new alarm system instead of the factory one I'm not sure if that's going to make your car more reliable on the grand scale of things?
     
  6. OP
    OP
    W140s500

    W140s500 Member

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    Car:
    Mercedes W140 S500L, W124 230 CE plus many more !!
    I was told by a Mercedes stores manager that the W140 was too complicated for it's own good !
     
  7. OP
    OP
    W140s500

    W140s500 Member

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    Mercedes W140 S500L, W124 230 CE plus many more !!
    Thank you, when I find out how to pm you I will send a email contact. Many thanks
     
  8. Dec

    Dec Hardcore MB Enthusiast

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    Are you in possession of any other remotes or odd looking keys similar to what’s in in the centre of the picture below?

    Dec

    [​IMG]
     
  9. grober

    grober MB Club Veteran

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    this is an excellent introduction to the W140 electronic systems. Altho it deals with A 1994 500 coupe the majority of electronic systems are the same.
    K6JRF Auto Page
     
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  10. OP
    OP
    W140s500

    W140s500 Member

    Messages:
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    Location:
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    Car:
    Mercedes W140 S500L, W124 230 CE plus many more !!
    I have one working key and a ' dead ' key also; those being the one button flip key. The Scorpion alarm fob is the same as my 92 W124 230 CE
     
  11. OP
    OP
    W140s500

    W140s500 Member

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    The K6JRF page is very informative and of great help :)
     
  12. OP
    OP
    W140s500

    W140s500 Member

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    Car:
    Mercedes W140 S500L, W124 230 CE plus many more !!
    Out of interest, how many W140 owners or technicians have experienced alarm or immobiliser failure on these cars ? I may be brave and try using her a little next year, but fear something daft like alarm or immobiliser lockout will leave me with a big headache.

    I know removing factory alarm systems isn't the done thing,but if it keeps a car alive isn't it better than ending it's life prematurely ?

    On the positive side of Mercedes ownership neither of our W124's have given us anything other than pure pleasure.

    Thank you for all your patience and understanding
     
  13. guydewdney

    guydewdney Hardcore MB Enthusiast

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    surely a w140 is old enough not to be a theft target any more? depends where you live i suppose.....

    my 140 never had any alarm problems. or any significant electrical issues. but it was a 1996 vintage.

    isnt there something like 'add a fuse into the ecu under the passenger footwell' which bypasses the immobiliser for 99 starts.?? or is that my imagination?
     
  14. Dec

    Dec Hardcore MB Enthusiast

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    Do you know if there is actually an alarm system fitted to the car, and in working order, either the aftermarket type like the Scorpion or a Mercedes system that would have been fitted at the factory?

    Dec
     
  15. OP
    OP
    W140s500

    W140s500 Member

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    Car:
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    There is an alarm as I have heard it go off when the cars battery when low once, which made the hazard lamps flash. I only have the one button key fob, and no secondary fob or over-ride key so believe it's factory standard
     
  16. OP
    OP
    W140s500

    W140s500 Member

    Messages:
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    Car:
    Mercedes W140 S500L, W124 230 CE plus many more !!
    I have heard of a 99 starts bypass before, but not sure exactly. I have also heard of finding the immobiliser unit under the steering column, and cutting and joining 2 pairs of coloured wires. I think with my luck I would probably cook the electrics !
     
  17. Dec

    Dec Hardcore MB Enthusiast

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    Put your VIN (located outside bottom of windscreen, passenger side) into the link below.

    Checking VIN for Mercedes-Benz | CARInfo

    Then scroll down to check if there is any mention of an alarm being fitted in the list of options.

    Dec
     
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  18. bolide

    bolide Hardcore MB Enthusiast

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    Assuming it's a similar setup to the system in a contemporary W124, there is more than one version of the RCL remote locking setup. The first just locks & unlocks, the second has an alarm & immobiliser and flashes the indicators when the alarm goes off, and the third is the ATA system. ATA has sensors on the stereo, a tilt sensor (though that may be an option) and a relay to cut the ignition system

    IIRC the relay is behind the binnacle. The RCL brain is usually under a back seat and the ATA brain is in the passenger footwell. The ATA brain has two pins that feed the ignition (and possibly fuel shutoff) relay

    Nick Froome
     
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  19. grober

    grober MB Club Veteran

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    Although this is for a coupe I doubt its different for the saloon K6JRF Auto Page
     
  20. grober

    grober MB Club Veteran

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    There were numerous changes to the wiring of these cars in the early days meaning they vary from year to year. Although the integration logic of modules remained basically the same their wiring implementation varied. This tends to preclude simple defeat wiring bypass strategies by rote/simple instructions. e.g. cut the red and yellow wire on the steering column or replace the blue link in the footwell. etc etc You might end up causing more problems. You need someone who is very familiar with how these systems work to apply that knowledge to your exact model. Because the car is so old now and was never very common these people tend to be very thin on the ground. :(

    s500 w140 no crank - PeachParts Mercedes ShopForum
     

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