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Audi CQ20V ABS problem

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  • Audi CQ20V ABS problem

    I have ABS problem on my CQ20V, when i start engine, after first brake push, the ABS light comes on gauges. Every 4 pieces of toothed wheel are new, ABS sensors are old. What gap is needed from sensor to toothed wheel?Is that copper/steel sensors sleeves necessary?I suspend that is the gap, what lights on a ABS control on gauges...

    And what about check resistance of sensors?What numbers might be turn around?

    Thanks
    Last edited by Tom_; 11th April 2017, 12:20. Reason: Change title
    Audi Coupe Quattro 2.3 20V

  • #2
    when you push the pedal to get the light on, has the car moved at all.

    If it's sitting stationary when you do this, it's not a sensor problem
    Mike

    http://www.s2-audi.co.uk

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    • #3
      I am not sure right now, i will checked later, but i am think thats doin when the car is moving...
      Audi Coupe Quattro 2.3 20V

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      • #4
        Guys, i change the bad 2 sensors, and still ABS lights ON after 3 minutes of driving...Any ideas?Because i measure the new sensors and torque the driveshafts and numbers was OK (changing). What about air buble in ABS? i really dont know why is doing that.
        Last edited by Tom_; 23rd March 2017, 16:46.
        Audi Coupe Quattro 2.3 20V

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        • #5
          I have a new 4 pieces of CV joints (so no rust anymore) New 2 sensors, measured a impendace (moving with shaft and changing numbers of impendace = new 2 sensors ok) and was ok, the old ones i only measured a impendace on connector and was good 1,2kOhms...so whats next? Its really pissed me off :/

          While drive LIGTS ABS ON i push 2 times (during driving) ABS swicth, than is about 1-2 minutes ok and than lights on again...

          And if i can push a ABS switch 2 times (while ABS light ON) i guess that the relay is good, because ABS lights off... its my theory right?
          Last edited by Tom_; 23rd March 2017, 17:23.
          Audi Coupe Quattro 2.3 20V

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          • #6
            Today i lift car,pull first gear and measure voltage on connectors of ABS sensors...everything pulls the same numbers,,,around 0,30-,050 on idle 1 gear. But i noticed, that ABS modul pump goes mad and very often "makes the pump sound" Heres the video (sry for clicking engine= was cold ) The second one from the interior, there was a huge interval of "pumping" at the end stop "pump". Any ideas whats gonna be?That ligthing ABS? Where is problems when sensors are good, teeth wheels are new..so no rust or debries..I look on ABS reles, but i didnt recognize any damage....






            Please help me
            Audi Coupe Quattro 2.3 20V

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            • #7
              Hello Tom,

              which measuring instrument did you use?
              Unfortunately i can't watch your videos.

              But I know how annoying it is, when the ABS-system doesn't work how it should
              I had nearly the same problem on both of my cars until I bought myself an oscilloscope.

              My Coupe always drove to the left while I used the brakes, until the ABS light came after I drove 500 meters.
              On my S2 Avant, the light was off all of the time, but always when I just touched the braking pedal, the system worked very hard, like I drove on snow

              Result after measuring:
              Coupe: ABS-sensor gap too big on the right side, therefore no signal (third pic)
              Avant: broken ring (first, second pic)

              The fourth pic shows, how the signals of left and right site (in this case first axle) should look like. You don't even have to use first or second gear. It's enough if you rotate one of the wheels with your hand. The other wheel will rotate at same speed, but in the other direction. Then you only have to compare the signals on the oscilloscope.

              If you act like workshop manual says, you have to push the sensors until it stops. There is no gap to look after.

              If you use an oscilloscope (at least 2 channels), it should be simple to find the problem.
              Attached Files
              '95 Audi S2 Avant
              '92 Audi Coupe T89 quattro 2.3E

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              • #8
                Hi Shorty,

                for measuring ABS sensor a normal multimeter. I measure a static (resistance) all sensors around 1,18 Ohms and than measure voltage and turning with wheels and every 4 sensor around 0,30 - 0,50...So u push it to the max (when it hears the sound when its just stopped)? And with that osciloscop u measure connector of ABS sensors?Or somwhere else?

                I measured it, exactly like as in the video

                Last edited by Tom_; 26th March 2017, 20:09.
                Audi Coupe Quattro 2.3 20V

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                • #9
                  In my opinion, a multimeter is too sluggish to measure the signals. Furthermore you can't compare two signals at the same time.

                  The value of the resistance is not very helpful in this case.
                  0.30 - 0.50 what?
                  Yes i push the sensors as much as possible. With your hand you will just be able to put it in the half way. I use a plastic hammer. But you have to be very careful. You will notice when the sensor has reached it's max.
                  And don't forget this part.

                  With the oscilloscope i always measure two sensor signals at the same time (therefore you have to use at least a 2 channel oscilloscope).
                  I got the signals directly of the connector at the ABS-ECU.
                  In case of the Avant, the ECU is next to the battery.
                  Coupes have the ECU under the rear bench. But I don't know the pin assignment of the connector by heart

                  I can't watch your videos, sorry.
                  '95 Audi S2 Avant
                  '92 Audi Coupe T89 quattro 2.3E

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                  • #10
                    0,30 - 0,50 Volts...So i try to borrow an osciloscop if someone have it. Yes coupe have ABS ECU under rear seat. I find abs wiring diagram on 1989 Audi 90, so maybe it will be the same. Or do you have a abs ecu wiring diagram? Thanks for help

                    edit : I think, that problem isnt that all 4 sensors are havent the same (sinusoid curve) but i think the main problem that u had, was the one sensor was too far, second havent tooth. If are sensors ok, and u measure voltage when u turn wheel, it means, that tha gap is ok. If it was too far you cant measure any numbers...just 0. Because amplitude and frequency (in my cas voltage) are rising with the wheel speed to some point
                    Last edited by Tom_; 26th March 2017, 21:12.
                    Audi Coupe Quattro 2.3 20V

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                    • #11
                      Yes I have one, but at the moment it's in my workshop

                      No, my sensor wasn't dead, the gap was too big. The sensor's voltage depends on wheel speed and sensor gap. Frequency depends on wheel speed and number of tooth.

                      But my problems should just show you, that an oscilloscope offers a better way for diagnosting the signals than a multimeter does.
                      If all four sensor show the same signal, you know that your hardware works and you can go on with checking the CPU and so on.

                      Edit: I don't know how often you work on car's electricity, but if you have fun with it, it's not a bad idea to buy a semi professional (pc) oscilloscope (for example peaktech or picoscope). They aren't really expensive at all. Measuring a lambda probe makes more sense with an oscilloscope than with a multimeter for example...
                      Last edited by shorty_94; 26th March 2017, 21:21.
                      '95 Audi S2 Avant
                      '92 Audi Coupe T89 quattro 2.3E

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                      • #12
                        Do you go to workshop this week ? I know, thanks for this advice, i defenitely try, if i can get some 2 channel osciloscope. I am curious how its gonna be. Any other ideas, what it could be?If the sensors are ok, i think that reles it couldnt be either, because if so, abs lights on whole time from beginning, isnt it?
                        Audi Coupe Quattro 2.3 20V

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                        • #13
                          Originally posted by Tom_ View Post
                          Do you go to workshop this week ?
                          Yes of courese
                          I have to reactivate my S2 until next saturday
                          What does your wiring diagram of the Audi 90 say?
                          If you tell me the pin numbers, I maybe can tell you if they are right. I think the left rear wheel sensor has the numbers 19 and 21
                          For diagnosting my '92 Coupe quattro and '95 S2 Avant, I used the the same pins for measuring it's voltage. Therfore it should be the same assignment at Audi 90.

                          The only fact I know is, that the light is on from the beginning, when one of the relais is missing.
                          '95 Audi S2 Avant
                          '92 Audi Coupe T89 quattro 2.3E

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                          • #14
                            I dont know, what he say, because he dont speak with me I am not sure if its the righ picture, but here we go So my thought about reles was good
                            Attached Files
                            Audi Coupe Quattro 2.3 20V

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                            • #15
                              Forget my post about pin 19 and 21

                              The diagram doesn't talk to me too, but it looks good, as far as I can remember
                              Yes you're statement about the relais was not wrong, but I wouldn't spend time with them at the moment
                              You should stop to change parts without having an idea if anything is wrong with them. This procedure gets very expensive, except you have a huge stock of parts
                              '95 Audi S2 Avant
                              '92 Audi Coupe T89 quattro 2.3E

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