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ABS light intermittently 850

posted by  toad850 on  Mon May 6 08:22 CST 2013
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last visit: Mon Dec 16 19:20 CST 2013
[RELATED]

I have a 1994 855T and the ABS/TRACS light comes on intermittently. The OBD calls out a 444 code. I have replaced the ABS relay on top of the ABS module and tried another ABS module as well. Fuses all check out.
The code says "no power supply to hydraulic modulator valves"
I know with most cars there are chronic areas of failure and I am wondering if I am missing something obvious. I replaced the ABS relay on the advice of my mechanic who is now retired. It was old anyway so no big deal.








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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    You also try cleaning all the sensors located at the wheel hubs!!



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Cleaning all the sensors fixed the problem. I don't know why the code said no voltage to the pump.
      Maybe a safety feature when the sensors respond intermittently. Thank you again!



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Did you pull out the sensors to clean them or did you did on the hub.

        I need to some brake work and I also need to clean the sensor.

        My thought is to spray the sensors with some brake cleaner and blow them dry.


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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Well it was fixed for about 20 miles. To make a long story short the real problem was the "brake pedal position sensor" mounted on the power brake booster. They are known to develop bad solder joints inside and become intermittent. There is a post on the internet that shows how to repair it. I bought a used power booster for $20 on ebay that had the sensor still on it and used that one. I have since repaired my original sensor for a spare.
        It is important when reading the codes to read ALL OF THEM! I only read the first one and that was part of the problem. Good luck with yours!



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          I've got to try this this weekend.
          Been watching those lights go on and off intermittently for about 2 years now.
          --
          "Differences of opinions should be tolerated, but not if they're too different" - Sharon Craig



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          Time to send the ABS brain to Victor Rocha http://www.rochatek.com/absmain.html perhaps? He has always come thru for me for not much $$.
          --
          The Family Fleet '90 745 16v; '90 745 GLE; 96 855T; 99 XC, collectively approaching 900,000mi and going strong.



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    The 1994-5 ABS modules seldom fail, but the wiring may have a problem. Do check and clean the plugs and then use a zip-tie to secure the wire to something stable, just so the plug doesn't get stressed.

    I wish my 1996 had a builtin code reader... My ABS light comes on every other time I start the engine, without fail.


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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Klaus, the Abs light was coming on quite often like yours.. I took apart the ABS relay Module and touched up the solder connections.. Did the trick for mine, no light for over a year..

      Bob 97 850glt 71 1800e



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        If I knew how to solder and what kind to use, I would start real soon. I am afraid I would overheat a diode or something fragile!

        I am currently contemplating replacing the air duct system, it is broken and there is no air flow. Some of the flaps are stuck and will not move. Arrrgh.


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