ABS Waveforms with the VP

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  • David Green
    Senior Member
    • Oct 2009
    • 382

    #16
    Audi ABS Scope Traces produced

    Hi Guys thanks for all your help very much appreciated. I have done what greasebob has said with the wiring and grounding of the scope. I have been out on a trial run to produce some scope traces from the ABS system. I don't know why the Audi manufacturer has wired together two ABS sensors on this model of car, the Right Hand Rear and the Right Hand Front are both connected at the same ECM (PCM) terminal 03?

    The scope traces were a little confusing at first, apparently the VP when pressing the 'S' button saves three shots of the same traces, which confused me, so I had to delete some mirror images of the same graphs.

    The graphs I have got look good now, but the voltages from the scope traces you will see that the GREEN trace voltages are always lower. All scope settings for each channel are and have been kept the same values for the tests.

    I am now wondering if the correct way to test these types of systems is to carryout one wheel at a time and then move onto the next?

    Have a look please advise.

    David
    Last edited by David Green; 10-30-2016, 01:06 PM.

    Comment

    • greasybob
      Senior Member
      • May 2008
      • 1590

      #17
      The difference in signal amplitude could be because of a difference of the air gap between the sensor and the tone ring, what ever type it uses, on the halfshaft, in the wheel bearing or on the brake rotor. Check to see if it is adjustable. Another possible cause could be a difference in the resistance in the sensor.

      Comment

      • David Green
        Senior Member
        • Oct 2009
        • 382

        #18
        The sensor air gaps are not adjustable on this model, and the last time I checked the free play in the wheel bearings I didn't notice any. Apparently this ABS problem has been on this vehicle for a seriously long time, and the fault does not appear until around 80MPH crusing on the motorway, which covers a few miles before a code and fault is set. Apart from the amplitude in comparisons across the axles, the signals appear OK, so as you say there maybe high resistance in the circuit which appears to have a low signal amplitude. The fault code is always the same Left Hand Rear Wheel Speed Sensor Ciruit that is registered, so it is definately that circuit which I now need to investigate, but now just hoping that something untowards is the cause and not the sensor, then I can save a bit of money because I don't get paid that much to start with

        David

        Comment

        • vasau
          Senior Member
          • Jul 2007
          • 119

          #19
          David Green, I'm glad you have learned the very important lesson in scoping.
          If you need an exact snapshot of a screen, make a movie of your waveform and then do the snapshots.

          Comment

          • hefaus
            Senior Member
            • Dec 2007
            • 435

            #20
            power wire

            Originally posted by David Green
            Thanks for that info, the VP in the UK does not arrive with instructions on how to set it up and use it. I know some other Countries get a manual to help learn about the VP and its use.

            I know about the ground plug in the top of the VP, but didn't understand how I was meant to ground the VP with the cables supplied when measuring sine waves for ABS sensors, I just used channel 01 and channel 02 and plugged a lead into each sensor at the ECM connector. Also the VP does not arrive with a power lead to connect to the CIG lighter or battery, so I assumed that snap on must have thought about this and understood that users would use the VP on the supplied batteries power only?

            Some of the leads supplied and not readily understood as to their use, by example, one lead has a yellow and black lead which go into a black connector, then three wires come out of this black connector on the other side, I think one is channel 01 and one is channel 02, and the remaining black lead is the ground?

            However I don't know the correct function of this lead because it is not clear where the third lead has gone or what it does because it does not come out of the black connector, therefore what I am saying is;

            Three leads into the connector from the VP, and two leads out to the vehicle for testing purposes?

            I checked the continuity with a meter and two black leads have continuity, and also one black lead with the yellow lead?

            David
            Hi David. Did your Solus Pro not come with a battery connect wire and a cig lighter connector. If so they will work on the Vantage Pro. I see you are having some fun now with your Vantage pro. Enjoy. Keep smiling

            Comment

            • JR-1
              Junior Member
              • Mar 2010
              • 10

              #21
              Hi guys, thanks also for the usefull information , i learn something everyday
              Good work David

              JR

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