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Mercedes 190D 2.5 ABS constantly light on

Discussion in 'Suspension, Steering & Brakes' started by dlicheri, Jan 11, 2017.

  1. dlicheri

    dlicheri Member

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    Your Mercedes:
    190D 1992 2.5D
    The ABS light on my 1992 mercedes 190D stays constantly on from when I turn the key. I start the car normally and light never goes out.

    Everything seems to work correctly, however, I have not had a chance or opportunity to test the ABS system. I have replaced the following :

    1. OVP relay
    2. ABS ECU

    I have cleaned terminals on relays located on ABC pump. Battery is fine and charges correctly. I have measured voltage while alternator is running and it is 14.2 volts.

    I have read through the various forums and infer from some of the issues that have been reported, that if the light never goes off it can only be the ECU, OVP relay or relays that are on pump.

    Does anyone have any info on how the system works and what phases it goes through on power up to full operation?

    thanks in advance ...
     
  2. bembo449

    bembo449 Senior Member

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    going to be an ABS sensor on the hub surely ? or a reluctor ring ( if they had them )
     
  3. umblecumbuz

    umblecumbuz Senior Member

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    Here's a strange thing. Apart from reading fault codes to help eliminate your ABS light, this might just help:

    My ABS light would not clear, no matter what I tried. My scanner showed other faults which I cleared, and the only one that kept recurring - apart from the persistent ABS light - was a gearbox code. The gearbox fault was a spin-off from the ABS system, so that didn't concern me too much.

    But, to get to the point, in desperation I unplugged the Maf while the engine was running and the ABS light vanished. I reconnected the Maf, cleared the gearbox code, and all has been well since.

    Don't ask me why this fixed the fault, because I don't understand it. I pass this little gem on in case it helps someone else.

    Umble
     
  4. Cole@MBS

    Cole@MBS Forum Supporter Authorised Forum Supporter

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    Pull the RPM sensors of the hubs and make sure there not filled with swafe, seen that before.......
     
  5. star

    star Forum Supporter Authorised Forum Supporter

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    The abs light should go out when the car is started. It does a self check at 3mph, only then will it trigger a sensor fault. If it stays on when the engine is started, you need to get it on an Bosch abs tester.
     
  6. OP
    dlicheri

    dlicheri Member

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    I was told that was the case, abs test happens when wheel start to spin. If light remains on it is something else. Doesanyoneknow what sort of tests it goes through on power up ?

    Is there a abs manual available anywhere? What would be good is some sort of diagram showing you how it all fits together. Is there anything else I can try ?

    Finally, I live in southgat north London. Is there a borsch abs tester in my area?

    Thanks in advance.
     
  7. star

    star Forum Supporter Authorised Forum Supporter

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    Check the relays under cover on pump. We have tester but there might be someone closer.
     
  8. OP
    dlicheri

    dlicheri Member

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    If the speed sensors are open or short circuit / disconnected would that cause abs light to stay on permanently?

    thx in advance ...
     
  9. OP
    dlicheri

    dlicheri Member

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    I have now tested the following :

    1. OVP relay (metered at pins and tried with power to solenoid)
    2. ABS ECU (tried replacement)
    3. metered speed sensors and they show a resistance of 1K Ohm
    4. tested relays on ABS pump (as in 1)

    Puzzled !
     
  10. umblecumbuz

    umblecumbuz Senior Member

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    Looks like you didn't get live readings from the speed sensors.
    Doing this would certainly help to eliminate them as a possible cause.

    Umble
     
  11. OP
    dlicheri

    dlicheri Member

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    removed both relays and powered solenoid with 12V. relay clicks. Circuit is open when off, and continuous when relay clicks. Also removed big connector on ABS pump, sprayed with WD 40 and refitted.

    I have not metered the rear speed sensor as I do not know where it is ...

    Looking like I may need to take the car to an abs specialist!
     
  12. MercSLK

    MercSLK Senior Member

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    I have emailed you with position of Rear ABS sensor.

    HTH

    MercSLK
     
  13. stwat

    stwat Senior Member

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    The rear sensor is in the differential.
     
  14. OP
    dlicheri

    dlicheri Member

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    Just wondering,

    I found a general overview coupled with a number of circuit diagrams of the ABS system and it looks like the OVP relay is the central link in everything. It seems to distribute power to the ecu, the two relays under pump (which power the solenoids as well as the pump).

    Should I not be able to hear pump pressurising when I turn on the ignition?

    I am starting to wonder whether I am getting power to pump and ECU ...
     
  15. brianbrian

    brianbrian Senior Member

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    Abs

    If you do need a complete abs unit, includes relays, 30.00 this includes postage.
     
  16. MercSLK

    MercSLK Senior Member

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    Email sent.

    HTH

    MercSLK
     
  17. MercSLK

    MercSLK Senior Member

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    Another email sent. Can't PM you because you don't have PM privileges yet. I think you have to have a number of posts before you can PM.

    HTH

    MercSLK
     
  18. OP
    dlicheri

    dlicheri Member

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    190D 1992 2.5D
    I have now tried all of the relays and jumped the respective connectors to ensure that a relay on is simulated. ABS light is constantly on. The only thing that I am now unsure about is the speed sensors.

    Does the ECU test the speed sensors when it boots? Will the ABS light on dash remain permanently on if the speed sensors are faulty?

    The only other thing I can try is to read the led codes, however, I cannot see a round connector that I should be plugging into on my 190D 2.5 diesel. Does it have one??
     
  19. OP
    dlicheri

    dlicheri Member

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    SOLVED - ABS light constantly on from ignition to driving

    folks,

    Problem was due to dirty ABS sensors on front wheels. The sensors are located behind disk and can be removed by undoing two allen socket bolts. Once out, use a wire brush and wd40 to clean them up. Replacing socket bolts if is recommended when refitting.

    My speed sensors were encrusted with metal filings and generally dirt. I did both sides and refitted them. Like magic, the ABS light went off and the ABS system is now working nominally.

    I was quite sceptical as to whether it would be down to dirty sensors. The dirt and metal filings must somehow alter the electrical characteristics of sensors that cause them to fail the start up tests that are carried out by ECU.

    Many thanks to :
    MercSLK
    brianbrian
    stwat
    umblecumbuz

    and anyone that I have missed, and if anyone needs an ECU or an OVP relay, I have a spare ...
     
  20. Cole@MBS

    Cole@MBS Forum Supporter Authorised Forum Supporter

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    Said this in post 4.........glad it worked for you.....
     

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