Trying to Achieve Wheel Sensor Square Wave?

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  • tandetransmission
    Junior Member
    • May 2011
    • 6

    Trying to Achieve Wheel Sensor Square Wave?

    Hey guys, fairly new to oscilloscope. We're a transmission specific shop and have had positive results with testing speed sensors.

    I have this 2007 Dodge Nitro (1D8GT58667W682760) that has intermittent right rear wheel sensor drop out. Before testing the suspect sensor I wanted to check a known good one. So I went to the left rear and cannot seem to achieve a square wave signal. I'm sure due to my lack of experience/knowledge.

    So I'll do my best to give the details of my settings. The sensors are two pin connectors. To my understating a 12v supply and a signal wire. On the left rear Pin 1 light green wire is the supply, and pin 2 green with stripe is the signal.

    I assumed with the key on, wheels turning I should achieve square wave. I'm assuming I should see a b+ square wave? Again I'm fairly green at this so just ask for the details that I left out. I would really appreciate some help on understanding this.
  • Crusty
    Senior Member
    • Dec 2007
    • 2450

    #2
    Depending on the type of sensor, there could be a "square wave" signal, OR, the signal could be a "sine wave" signal. Some also simply put out a variable voltage.
    Sorry I don't have a definative answer for you. Check for some hints as to what kind of signal you should expect by reading up on the Dodge wheel speed sensor possible code sets.
    Also there are dome articles on various WSS designs in trade publications such as Motor-Age and Motor magazines
    Check all three of the other wheels and you'll probably be able to figure it out.

    Comment

    • Witsend
      Banned
      • Nov 2012
      • 2942

      #3
      With both rear wheel sensors disconnected and key on , I would see what the voltage supply at the lt green wire and yellow wire on the other side.If it is 12 V supply , I can't see any harm in load testing the yellow 12V supply side with a test light.(if you don't spread terminal) If it lights try the green wire and wiggle the harness where it flexs with the suspension to see if the test light flashes or goes out. Take your DVOM and compare sensor resistance from left side one to right side one, and disconnected , and that the suspect side measures no continuity to ground if the working side doesn't .Check for play in the bearings, compare your square wave pattern and voltage height on the return side of both side sensors after you ohm test and compare both sides return wires resistance between the connector and a good ground. If the suspect side return wire is shorted to ground you would not see a square wave on your scope while the the harness connector is attached to sensor and backprobed if return wire is shorted to ground. The next step would be to test for continuity of suspect return wire or connector terminal of ABS module which may be more sucky to have to do.

      Comment

      • BMW JEDI
        Senior Member
        • Feb 2012
        • 422

        #4
        The information for this WSS is available on the Snap-on scopes under 'Guided Component Tests'.

        Two pins, pin 1 is 12v supply and pin 2 is the signal.

        Connect B+ scope lead to Pin 2 (signal) and B- scope lead to a known good ground.

        Waveform is a varying frequency (with wheel speed) square wave with a max voltage between 0.8v and 1.6v.

        Comment

        • Steve6911
          Moderator
          • Feb 2007
          • 2168

          #5
          James

          Not sure what kind of scope you are using, this is from my Verus. It has LOTS of info for new users! The Modis Ultra or the Vantage Pro will do the same.

          20160120-1328-1.jpg

          20160120-1329-1.jpg


          Steve

          Comment

          • Steve6911
            Moderator
            • Feb 2007
            • 2168

            #6
            Sorry, Forgot this one

            20160120-1334-1.jpg

            Comment

            • Witsend
              Banned
              • Nov 2012
              • 2942

              #7
              That's all fine and dandy with the guided description but if you just back probed the connector of the sensor with the verus a good sensor will still likely look dead as a door nail with either an open supply wire or a grounded (shorted)return wire. A lack of any voltage should prompt you to check these, LOL

              Comment

              • tandetransmission
                Junior Member
                • May 2011
                • 6

                #8
                Thank you all for the responses. Sorry I forgot to mention which device I'm using. I too am using the Verus and I followed the "Guided Component Tests". Also keep in mind that I'm checking at one of the known good sensors. I usually go that route to get visual of what I should expect to see. But yet I still cannot achieve square wave. Haven't attempted to check the bad one yet.


                Something tells me I'm not hooked up right or something. Going to start from the beginning.
                I'll report back.
                Thanks again.
                James

                Comment

                • scottmechanics
                  Member
                  • Jun 2013
                  • 42

                  #9
                  Abs sensor test

                  Hello
                  Here is a YouTube vid on abs sensor using a verus and a modis
                  Hope it helps

                  Comment

                  • snapon20r
                    Junior Member
                    • Jan 2012
                    • 20

                    #10
                    what do you have your scope settings set to??

                    Comment

                    • greasybob
                      Senior Member
                      • May 2008
                      • 1590

                      #11
                      Try a 5 volt setting with a 5 second sweep with the filter on for the signature test.

                      Comment

                      • scottmechanics
                        Member
                        • Jun 2013
                        • 42

                        #12
                        Accoupling

                        Hello setting is on lab scope 1v with AC coupling
                        I think it is shown on the YouTube vid

                        Comment

                        • greasybob
                          Senior Member
                          • May 2008
                          • 1590

                          #13
                          scottmechanics you is correct. I tested an 07 Chrylser Town and Country today to see about getting a known good signal from the ABS speed sensor. This vehicle uses the Type 2 sensor where the 12 volt supply wire to the sensor is also the signal wire. The sensor drops the voltage only slightly as you can see in the 20 volt screen shot below. You are correct in that the signal shows up much better if you use a lower voltage setting and use AC coupling as seen in the 500mv screen shot below. The module also looks at amperage but the low amp probe in its best resolution can barely show it. It should also be noted that the Snap ON component test in the Vantage Ultra has the wrong info for this vehicle. it should at least have the info for the Type 1 and Type 2 sensors.
                          Attached Files

                          Comment

                          • Crusty
                            Senior Member
                            • Dec 2007
                            • 2450

                            #14
                            As in Steve's post, the amperage indicated could be as low as 0.007 to 0.014 amps.

                            A little frustrating when service information tells us that the amperage change is what the module is looking for, and our low amps probe has a bias of 10ma AND a "float" of another 10ma. With nothing hooked up, the signal could show 10ma (even after setting zero, again, and again) and pop up to 21 or 22ma on it's own.
                            I was told that 10ma is "negligable" which is not true when we're looking at signals this small. (this lack of accuracy also makes the low amps probe questionable when searching for parasitic drain measurements).

                            When looking for small signal changes, sometimes the "auto-find" feature can get us close and we can adjust the signal amplitude and time base on our own so we can make sense of a good signal to compare to a suspect signal.

                            Quite often, the help section of the tools is NOT correct, and as such, it can't be relied upon.

                            Sometimes systems use the same type of signal many years in a row, then suddenly change, and the information gets copied and pasted, incorrectly for the particular application or model year.

                            Even connector pin outs can be misleading. IF a service information such as Mitchell, or Alldata, or Identaguess shows the same configuration, we can use what is in the tools as a starting point. Even they are incorrect at times.

                            Samples and settings for all the possible sensor configurations should be illustrated, voltages, amperages, A/C coupling or not, square wave, sine wave, whatever may be possible.

                            Even better is for each tech to find and save "known good" values for himself on whatever systems he happens to see.

                            It is helpful when you post up some examples on here Bob. Gets people used to the idea that changing settings to something we may not expect actually reveals a valid signal trace.

                            Comment

                            • Witsend
                              Banned
                              • Nov 2012
                              • 2942

                              #15
                              Root Canal or Implant?

                              Had a 2005 AWD Ford Edge up on stands with a howling right rear hub, a bad Right front ball joint, a broken right front stab link, with a code for LF wheel speed sensor in memory . When road tested it had a false ABS activation about half the time at lower speeds. My scan tool graphing didn't pick out any drop out of wheel speed.I was ready to scope the sensor out , on the stands with my Counselor 2 but an inspection of the axle tone wheel and the problem was obvious. The left front axle needs a damn extraction. Customer declined, having no money to fix car till after tax refund. Charged a half hour labor and even showed the customer which fuse to pull for the ABS .

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