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Thread: ABS Return Pump

  1. #1
    Join Date
    Oct 2007
    Location
    St Albans, UK
    Posts
    530
    My Cars
    1991 850i

    ABS Return Pump

    Hi 8ers,

    It's been a long old while since I posted here, but I am hoping my american brothers will still come through for me.

    My 1991 850i has suffered from intermittent ABS and ASC light coming on after the car goes above about 5mph for a long while. Normally a restart solved it. The car sat for about 4 years slowly dying but last year i piled a huge amount of cash into it and now it's back up and running sporting new suspension front and back, new fuel and brake lines, brakes, lots of other stuff. Since it's been back on the road the ABS and ASC lights have come on again at 5mph, and now a restart doesn't fix the problem.

    I've already cleaned the abs sensors and flushed and bled the pentosin system to no avail.

    My DIS laptop can't read the ABS or ASC modules but the stomp test shows 15 flashes, which is "ABS return pump failure". Sounds pretty clear, but what isn't clear is what to do about it.

    The ETM has this:
    asc2.png

    When it refers to the ABS Hydraulic Unit, is that the "block" that sits by the brake bomb at the front left corner of the car, or is it the other ASC+T unit that sits below the brake master cylinder?

    Also, Timm (thanks for your help mate) suggested tripping relay K94 that should manually run the pump, but where is that on the early V12s? Timm's relay finder has it in a box that doesn't exist in my car.

    All help appreciated.

  2. #2
    Join Date
    Jun 2008
    Location
    N/A
    Posts
    2,798
    My Cars
    TT Cayenne / SC 850
    In my experience it is usually asc+t pump, rarely if ever abs pumps go out.
    Wither way, let me know if you need either, I have both in europe.

    Sent from my SM-G892U using Tapatalk

  3. #3
    Join Date
    Oct 2007
    Location
    St Albans, UK
    Posts
    530
    My Cars
    1991 850i
    Thanks Dragon. Is there a way to work out which unit the fault is referring to? They both look like an absolute mission to replace so I don't want to guess.

  4. #4
    Join Date
    Jun 2008
    Location
    N/A
    Posts
    2,798
    My Cars
    TT Cayenne / SC 850
    Quote Originally Posted by NickF View Post
    Thanks Dragon. Is there a way to work out which unit the fault is referring to? They both look like an absolute mission to replace so I don't want to guess.
    Remove the headlight and inspect all the wiring to ABS unit, I have repaired some wires down there chewed up by mice. If all the wiring is good I would say asc+t pump needs replacing.

  5. #5
    Join Date
    Oct 2007
    Location
    St Albans, UK
    Posts
    530
    My Cars
    1991 850i
    Thanks Dragon. I'll give that a go at the weekend.

  6. #6
    Join Date
    Jun 2012
    Location
    Uk
    Posts
    1,287
    My Cars
    1994 850csi rhd
    You can fire up the abs pump manually if you pull up the drivers side carpet nest to the seat (LHD) pull the connector out of the ABS controller and link the power wires to the motor pins. I think I have some photos on how to do this in my "Live mapping CSI" thread My pump motor had rusted into place, you can remove 2 screws and pull the motor out of the pump body, clean and reassemble.

  7. #7
    Join Date
    Jun 2012
    Location
    Uk
    Posts
    1,287
    My Cars
    1994 850csi rhd
    Here you go
    Attached Images Attached Images

  8. #8
    Join Date
    Oct 2007
    Location
    St Albans, UK
    Posts
    530
    My Cars
    1991 850i
    Thanks Omega Man. I'll let you know how I get on.

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