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  • Abs fault

    Have a quattro coupe 20v. Abs light stays on, car not even moving. Drive down the road and it flickers and blinks sometimes not for very long sometimes stays on for ages but eventually goes out. All wheel sensors are in good order abs switch doesn't work. Doesn't stay in when pressed so I need another one of them. Anyway I'm thinking itsi a relay. Suspect one that's behind the panel underneath the steering wheel. Please anyone any ideas please. Does anyone know if the relays and abs switch are still available. Thanks All help and any help greatly relieved.

  • #2
    ABS switch is not supposed to stay in, it is a momentary switch. You can bridge the abs combi relay 76 with a piece of wire to eliminate switch and combi relay fault.

    https://www.s2forum.com/forum/techni...0v-abs-problem
    1989 Audi 80 Quattro
    1994 Audi 80 Quattro Competition

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    • #3
      Thanks for that. Thought it strange that it didn't stay in so assumed it was broken. As for abs light staying on its doing my head in because that is an MOT failure.

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      • #4
        The best circuit I have to hand for that is here --> http://www.s2central.com/S2_Schematics/D/D26.pdf - I can have a quick look for any suggestions, but your 20VCQ could have slightly older version of this circuit with some differences that could be negligible or significant.
        Paul Nugent
        Webmaster http://S2central.net
        Administrator http://S2forum.com

        1994 S2 Coupe ABY - aka Project Lazarus
        2001 A6 allroad 2.5TDi - family tank
        2003 S4 Avant 4.2 V8 - daily burble

        Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

        There are only 10 kinds of people that understand binary - those that do, and those that don't

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        • #5
          So a very quick summary of this...

          The master control unit is J104 under the rear seat - this generation of system has no OBD comms unfortunately
          Main control relays (J105 & J106) are sited on top of the hydraulic module - you should see a cover that can be removed to find part numbers on the relays and access pins below for test etc.
          There is also the 'combi' relay J156 under the rear seat in the little auxiliary holder there at position 22 - this is part of the circuit with E83 switch for turning ABS on or off

          Do the basics first - check the earth points and that fuse 31 is good.

          Remember the diff lock controller can also tell the ABS controller to stop working - you haven't left the diff lock switch on ?
          More explicitly on that its F100 - the switch inside the rear diff - that signals to the combi-relay if the diff is locked - see track 47 and follow that br/sw wire to track 30 - if that pin on the combi relay is 0V then ABS is turned off as it thinks the rear diff is locked.
          Paul Nugent
          Webmaster http://S2central.net
          Administrator http://S2forum.com

          1994 S2 Coupe ABY - aka Project Lazarus
          2001 A6 allroad 2.5TDi - family tank
          2003 S4 Avant 4.2 V8 - daily burble

          Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

          There are only 10 kinds of people that understand binary - those that do, and those that don't

          Comment


          • #6
            To check the combo-relay (J156) I would suggest the following:

            Permanent 12V at pin 2 (ro) - frighteningly this isn't fused by the way !
            Key ON - should see 12V at pin 5 on sw/bl wire (via Fuse 31)
            0V at pin 4 (br)
            You want to see pin 1 (br/sw) open circuit (unless the diff is locked and it switches to 0V)
            Pin 6 (sw/bl) should also be 12V when Key in ON, unless diff is locked or the ABS cancel switch has been pressed

            If the ABS controller is getting powered up correctly you should see 12V on its Pin #1 - that same sw/bl wire from the combi-relay
            The actuation of the ABS warning lamp in the dashboard is determined by status of pins 29 and 32 on the ABS controller. I don't have an official document on this but given the use of a diode within the hydraulic unit (N55) to verify there is electrical connectivity from that to the ABS controller. That suggests to me that pin 29 (and 32) would be switched to 0V if the controller is unhappy with something. Only when the ABS controller declares happy does pins 29 and 32 go into high impedance state (or switched to 12V) to stop current flowing in K47 i.e. turn of the ABS warning lamp

            PS - I am using same colour codes above in German as the Audi schematics and your colours for older 20VCQ could be different !!!!!
            ro=red (rot)
            sw=black (schwartz)
            bl=blue (blau)
            br=brown (brun)
            Paul Nugent
            Webmaster http://S2central.net
            Administrator http://S2forum.com

            1994 S2 Coupe ABY - aka Project Lazarus
            2001 A6 allroad 2.5TDi - family tank
            2003 S4 Avant 4.2 V8 - daily burble

            Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

            There are only 10 kinds of people that understand binary - those that do, and those that don't

            Comment


            • #7
              Originally posted by studley07 View Post
              Thanks for that. Thought it strange that it didn't stay in so assumed it was broken. As for abs light staying on its doing my head in because that is an MOT failure.
              It is not a fix, but there are timer circuits, remove the bulb and use 12V led with this circuit

              https://www.ebay.co.uk/itm/MINI-SMD-...-/280819762656

              1989 Audi 80 Quattro
              1994 Audi 80 Quattro Competition

              Comment


              • #8
                And to verify you have some connectivity from J105 and J106 relays into J104 (the main ABS controller under the rear seat) you should see pretty much 12V at pins 27 & 28 on the ABS controller as there is only the relay solenoid resistance between 12V (ignition ON) and these ABS pins - they presumably get switched to 0V when ABS activates.

                Lets look at J105 now - this one drives V39 - the ABS return flow pump. When pin 85 on this relay (which is a normal SPST device by looks of things - but with high current capability) is pulled to 0V by the ABS controller pin 28, the pump is ON.

                For J106 the operation is very similar except its an SPDT relay which places 12V across all three solenoid valves (in the hydraulic unit) when the ABS controller activates pin 85 of the relay when it pulls ABS controller pin 27 to 0V.

                With suitably beefy jumper wires you can manually hacktivate all the components in the hydraulic unit - safest to do that with ABS controller unplugged.

                Also worth checking the impedance from pins 2, 18 and 35 from the ABS controller to 0V - they should be broadly the same when J106 is plugged in - this verifies the electrical resistance on each of the three solenoid valves - if one of those is too high or too low the ABS controller might declare a fault.
                Paul Nugent
                Webmaster http://S2central.net
                Administrator http://S2forum.com

                1994 S2 Coupe ABY - aka Project Lazarus
                2001 A6 allroad 2.5TDi - family tank
                2003 S4 Avant 4.2 V8 - daily burble

                Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

                There are only 10 kinds of people that understand binary - those that do, and those that don't

                Comment


                • #9
                  I just checked out the other current thread about CQ20V ABS problems - someone shared an aftermarket wiring diagram for the 1989/90 B3 quattro ABS circuit and some notes have to be made in comparison with the 'D26' schematic that I linked above from MY92 3B Coupe.

                  Electrically speaking the schematics are identical with the exception of pins 22,23 on the ABS control unit - different pins are referenced on the 3B diagram that I linked. The wire colours seem to match perfectly.

                  MOST importantly, the pin numbering on the hydraulic unit is very different between the two diagrams, but the actual connectivity to the relays and solenoids is the same.
                  Attached Files
                  Paul Nugent
                  Webmaster http://S2central.net
                  Administrator http://S2forum.com

                  1994 S2 Coupe ABY - aka Project Lazarus
                  2001 A6 allroad 2.5TDi - family tank
                  2003 S4 Avant 4.2 V8 - daily burble

                  Purveyor of HomeFries and Exclusive agent for Samco hose kits (S2/RS2)

                  There are only 10 kinds of people that understand binary - those that do, and those that don't

                  Comment

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