How to test a digital ABS wheel speed sensor - 08 Chrysler,Dodge,Jeep

hey guys this video coming up this is on a 2008 jeep commander with an ABS wheel speed sensor fault and it is another magneto resistive type and so the first thing that I would suggest you do before you watch this one is watch the 2006 Chevy Colorado magneto resistive type wheel speed sensor video that I just shot and I'll put a link in the video too and again I will put it in the video itself so don't turn the captions off because you will miss the links and important notes that I put in my videos and you know I've had some comments when people don't like that but you know you want it in the description but truthfully it's better in the video because I can put a note in exactly where I'm talking and make corrections because yeah I definitely make some some mistakes when I'm speaking sometimes so those captions are useful for me to correct that but I will put a link in to the other video that I'm mentioning right now but with this 2008 jeep it is completely different than the Colorado and I think it's worth watching this video the format's a little bit different I actually took some still photos of our testing points in the speed sensor itself and then we we brought everything into the classroom and we talked about it on the smart board it just allowed me to go through everything a little bit more thoroughly with my class and it's a little bit long but I think it's worth watching hope you guys enjoyed I'm not sure the best way to introduce this but what we're going to talk about is a 2008 Jeep Commander ABS wheel speed sensor problem that we had in here the other day and I can get you up I guess a picture of the hub so this is the left rear that we're looking at typical speed sensor reluctor inside of this hub assembly pretty small teeth on this one one of the things that that we noticed and it was a I believe it was a left rear speed sensor circuit that was the default code we had so one of the things that we did is we went to Mitchell and we looked up our flow chart before we go through this flow tour because that's pretty much the last thing that we like to do in most circumstances you use the manufacture flow chart we back probed the terminals on the speed sensor to see what type of sensor it was and what type of signals we had this is what we had on one of the two terminals was 10.5 volts and if you remember from the last magneto resistive digital type speed sensor that we did what we said is when you have battery voltage on one of the two wires near battery voltage on one of the two wires on a BF speed sensor it is a digital type it's not going to be a variable reluctance sensor one that makes its own voltage so this one's going to be a digital signal what tells us that the fact that one of these two has battery voltage when we spun the wheel nothing changed it stayed flat initially is that correct it was initially flatline on that no change whatsoever then we back probe the other wire and it looked like this flatline zero all the time spun the wheel we have nothing so now we're left with what's the problem is it wiring is it the sensor is it the computer we need a little bit more help if this is anything like the last one if you remember the sensor generates a low voltage signal and it was somewhere around 0.8 to 1.8 volts was what we saw on the last case study that we did that was a 2006 Chevy Colorado and then we had one previous to that or I mentioned one previous to that that I did on an O for Chrysler that was exactly like that Colorado same low voltage signal and what we were looking for is on this wire right here the one that read zero we expected to see a signal and we did not so what we did is we went next before we did all kinds of homework we went to the right rear to compare a known good one we know we have a signal on the right rear sensor and we took a look at the right rear so let me give you the pictures of the right rear of the initial pictures this is the feed wire we could call it battery supply wire to the right rear sensor while we were spinning the wheel we know we have a signal on this thing because we see on the scan data a mile prior reading what do we see here a little bit of oscillations in this signal very very small and if you look at the min/max voltage may be around four hundred millivolts different so I'm looking right here there's ten point four and and ten point eight so around four hundred millivolts you can barely see some oscillations in here these up downs then we went to the what we thought we still think this is the supply then we went to what we thought was the signal wire and again it looked like this on the right rear a known good working circuit this is night and day different isn't it from our 2006 Colorado our 2004 Chrysler this is night and day different and I say night day different because here's what we had on those ones on the 2006 Colorado and the 2004 Chrysler what we had on the speed sensor circuit on the supply we had somewhere between 10 and 11 volts and on the signal we had somewhere between around a half a volt to one and a half volts somewhere in that range I think this Oh for video that I did the numbers were a little bit off from that and this circuit right here this half a volt one and a half hole there was a small square wave that would occur on that circuit so that means that this is the signal wire and this is our battery positive or supply wire that's what we had on the last two that we did this 2008 is not like that this 2008 commander again what we had was a very small oscillation we were ten point four to ten point eight on what's called the supply wire this is the actual wiring diagram for this color for this 2008 this is my 2008 jeep wiring diagram jeep commander and notice this second wire right here guys with this wire right here what are they calling this inside can you see it left front I know I'm on the left front I'm sorry I've sort of made that clear I showing all four speed sensors here it doesn't matter if it's left front left rear whatever for the diagram we're dealing with the left rear it's the same thing for the left rear so just bear with me with that but look what it says left rear wheel speed sensor signal is that opposite wire we're not seeing that are we this was our initial thoughts with this is we have no signal here so on a working sensor again we have no signal in this wire it is flatline zero volts and on this wire we have a very small 400 millivolt change as the wheel is turning so we assume and I think assume correctly that this one is different than the last one and it looks like our signal is on the supply side our wiring diagram to me that is wrong next thing we tried to do is we try to do an amperage measurement not have read in some other material that these things produce a small milliamp reading that the computer monitors and the numbers that I read was 7 milliamps 214 million that the computer will see changes as the wheel terminals you read some material it says that it monitors voltage and current now 7 milliamps is a really small number what we tried to do unsuccessfully is to put an amp clamp around the wire and measure it my lowest amp setting I believe is 100 milliamps on the ammeter on the inductive ammeter I might be wrong on that here's the thing I couldn't see anything and when you use an inductive ammeter on that low of a scale there's all kinds of noise and hafs in there there's no way you're going to see that we couldn't see any amperage measuring it that way so do you guys understand where we are with this Jeep right now we're a little bit unsure of how it works we think that we have a signal on the supply side why is all the material telling us differently this being one of them the wiring diagram is telling us the signal is the opposite wire as the supply so we got a little further help and what I did is I took some captures of the component test meter of the vantage prep so I want to walk you through that so we went to the component test meter of the Vantage Pro again looking for some help how does the sensor function what should we be seeing and I don't know if I did this with you guys yet I don't think I did notice down here 2008 commander that is my vehicle and working on it gives me a little bit of description operation I think that's where I'm at first with this first capture is that says the cab sends 12 volts to the sense of the cab is the anti-lock brake control module and the sensor has an internal magneto resistance bridge so okay that helps this is definitely going to be a digital we already know that by voltage readings that we had voltage it says that alters voltage and amperage of the circuit so we're looking at both shows me the connector harness I'd back probing next picture I expanded this box so this box right here I'm just opening that box up on this next picture and this is what we see so we left off amperage alters voltage and amperage of the signal circuit voltage and amperage is changed by magnetic induction when tooth tone wheel passes the speed sensor says a square wave digital signal that varies from point eight to one point six volts is sent to the cab I'm smiling here because this is not what we see is it this is what we saw on the Colorado this is what we saw on the older Chrysler video that I did but this is not what I see on this vehicle then it went through some of the pinpoint tests or the component test specifics and I went to DC voltage it's telling me how to connect my leads known good ground will speed sensor signal okay which one's the signal right let's go back notice right here one and two will speed sensor 12 volt supply will speed sensor signal if you guys were working on one of these on your own without any kind of help without any kind of knowledge previous to these sensors what are you thinking my supply is separate from my signal and that what do we have we had ten ten point four ten point eight volts as we're spinning the wheel and zero on the one wire what do we think of that one wine that is our signal this is a problem this is where we are with this vehicle now imagine if you didn't have a known good vehicle to go by sorry I imagine if you didn't have a known goodwill to check and this is all you had you're in trouble this information is bad hopefully snap one fixes this I'm sure they will I'll let them know maybe the next update they'll they'll change this but I'm going to show you it's not just Snapple and that's wrong on the sensor or manufacturer flowchart that Mitchell copies from them is also wrong on this car you saw the diagram was wrong too so what you go going through the tests again wheel speed sensor signal we are assuming because of this that it is separate from the supply so we connect to it it's telling me again to look for a point eight to one point six volt square wave and it gives me basically what signal should look like we're not seeing any of this and those were under wheel speed sensors for the Oh 8 commander and I think what I did is I changed the years to see if this changed but maybe we're off a year so I advanced it a couple years and I went back a couple years to get descriptions so sometimes that happens we've seen that our 3-part case study we did with the computer that had an issue in the battery that exploded we ended up using a diagram to find our parasitic drain on the next year up right so we have that sometimes that was my thought process going through this well maybe we're just off a year so look I picked an O seven commander what do we have point eight to one point six I'm looking right here same information oh seven commander oh six I go a little further I notice in the description in an oh six commander that that information isn't there it talks about what it does it alters voltage and amperage but it doesn't give me a number and I'm like okay cool maybe we found right they we found a different design here so I go further into this one and I go to the DC voltage test on the O six commander and look what it tells me again point eight to one point six on the signal that's not what we have so at this point doing research I kind of have to now I need some more info on the sensor are you guys on the same page with me here we have some discrepancies all of the material that I found on this vehicle so far doesn't match what we have so let's let's use the float art now maybe the flow chart from the manufacturer is going to help us and then let's look at the wiring diagram to which that wiring diagram really wasn't helpful was it the wiring diagram from the manufacturer again Mitchell redraws them they're calling this signal right here the signal is separate from the sensor supply not what I'm seeing so let's do the flow chart together we'll see what where we go with this our code was our C 1020 right was it 10 20 code you remember left rear wheel speed sensor circuit so I'm clicked on the left rear wheel speed sensor circuit code we start over here on the left hand side and we have a circuit schematic we can click on that and all that is is I've done that already figure 20 to make this a little bit easier and find that figure there's figure 22 this is your this is your wiring diagram from the factory courtesy of who courtesy of Chrysler wiring diagram for this wheel speed sensor and it doesn't matter which one we pick mm-hmm left rear right rear well let's stay with the left rear because this is our fault code what do we see right here I don't know in fact that's clear to you guys that says left rear wheel speed sensor supply okay cool and that says left rear wheel speed sensor signal I don't know if you guys feel like I feel right now but this is the kind of crap that we've been dealing with for while at least the 20 years that I've been doing this we use this stuff as a guide but then this is our only guide and it's wrong this information is wrong I'm going to show you that as we continue the supply is not separate from the signal as this is stated okay let's keep going let's go to this back to the flow chart so that was our figure 22 additional or circuit schematic we just looked at additional wiring that's just the whole system diagram and that would be this one but that would be this one that I showed you guys that's the additional diagram so it's the same crap in the additional diagram then it gives me stuff monitored condition set conditions possible cause I like possible causes that's cool this is what we use these flowcharts wiring harness terminal connector supply wheel speed sensor signal circuits sorted to voltage Brown or open left wheel speed sensor signal circuit sorted to left rear wheel speed sensor supply so again what is this implying in our possible causes our signal is separate from the supply okay saying that's wrong diagnostic tests going down a little further check DTC left ER will speed sensor circuit it's there it's there all the time these first couple of steps is is reading recording and checking to make sure that it's displaying that code and it is so we go to step two check connector terminal four dams okay great they're having you do a visual inspection we can all do that look at make sure your pins aren't bent damaged okay from there if it's still not you don't see a problem there we go to step three what do we do next check left rear wheel speed sensor 12 volt supply circuit for voltage they're having us disconnect the sensor turn the ignition on measure your supply voltage is it above 10 volts was it ours above 10 we were 10 4 - 10 8 right when we were moving the wheel on our vehicle that was dead I think it was around 10 8 and by the way as we continue throughout the day we were messing around with this battery voltage was dropping system voltage was dropping so I think at one point time we were down to around 7 volts and then we realized hey our battery's dead on the car so that voltage is a factor of system voltage to keep that month did we have a 10 volt supply yes we did so where do we go if we have a 10 volt supply on this float or we we go to step 6 that make sense we're skipping step forward we're not worried about short to ground on the supply we're going right to step 6 because we have voltage step 6 says to check the left rear wheel speed sensor sorry signal circuit signal circuit is that the same wire for us separate water foot worth it's a separate water so now we're on the other wire to the speed signs what are we doing now check for a short to ground on the left rear wheel speed sensor circuit what are we doing with this sort to ground test figure 26 shows us a picture look use 12 volt test line connected to 12 volts it doesn't say what kind of tests light does an LED regular incandescent I think that makes me feel a little more comfortable about what I did on the older Christ are using a incandescent style test like doing some bypass testing anyway use it using a 12 volt test light connect to 12 volts um I'm looking right here we are going to probe the left rear wheel speed sensor circuit so let's get a picture what that looks like this figure 26 I have that captured here let's give you figure 26 there's figure 26 what are we doing disconnecting the sensor we are taking a test light to battery pause and we are touching on pin two which is the signal for the sensor okay we did that what are the tests light do we test light lit and it looked very brightly and we were using a regular incandescent style light actually I think we use both we tried an LED light and my concern with the LED light was well maybe it's finding a path through the computer and it's not shorted to ground that's where we're at didn't matter we put a incandescent style in there and it lit very brightly too so let's go back to the flow chart does the test light illuminate brightly what's the what we do here guys repair repair the left rear wheel speed sensor signal circuit for a short to ground are we losing right now if you are going to follow this manufacture flowchart for this vehicle you are losing money because what are you going to be doing now for the rest of the day this circuit shorted to ground that's it they don't give you anything else for that repair this circuit for a short to ground so let me give you an idea what this might look like you're at the sensor we've identified which one the signal is we've identified which one the feed is we said our supply circuit is good right we measured down here we had 10 plus volts we're measuring over here it's at zero all the time so the next thing that we have done is we have removed the sensor ok and we've taken a test light here connected to battery positive test light is light test light is lit short to ground that's what the flow chart has us do it repair the circuit for a short to ground how would you do that well myself with the cab still connected that's our anti-lock brake control module wouldn't we disconnect the module and didn't tell us how to repair the short to ground I assume from the manufacturer they expect you to know how to do that short to ground if it's me I'm going to do this next step I'm going to unplug the cab and I'm going to watch my test line ok if I am tug the cab and the test light stays lit hope what you guys think about the wiring no question short to ground find it and that short the ground could be anywhere in that harness it doesn't matter where that sort is it's going to light the light no matter where you put the light on the circuit that light will light all the way across doesn't matter it found a ground fix it I don't have an answer for you there do some visual inspections running a new wire from the sensor to the computer is not an option let's fix what is damaged because in this field when you find one wire that's damaged guess what you usually find another one in that same area we want to find where it's damaged ok so let's say that when we on let's say when we unplug the the computer that my test light goes out what are you thinking it's not a short to ground on the wire would you agree with me it's not a short to ground so what does that lead us to a computer problem what will you possibly do if you follow this manufacturer flowchart what will you possibly do in this step you might replace the computer thank goodness we have three other wheels that have the same circuit wouldn't you agree that when you have an ABS problem on a single wheel you better be looking at these other wheels to help you what did we do we looked at the right rear and we did not see what they're telling us we should see and yet the right rear functioned and the computer was able to read the right rear signal that kept us from getting in trouble if you jumped at this car and follow the flow tarp you lost on this job this is not how the sensor works so let me do the best I can and show you what we found yesterday when we measured the circuit like it should be measured questions so far doesn't it suck before I do that just want to talk about this again these manufacture flowcharts I don't want to convey the wrong message that that they're all bad we need these flowcharts to help us there's a lot of good flowcharts out there but at the same time there's a lot of bad ones and what we need to do to avoid this pitfall is we need to know circuit design don't you think that in this application circuit design is everything if we know how the circuit works what it should look like will that keep us from getting in trouble following a bad flow term and the answer is yes so part of that is going to be being willing to do research what kind of research well we use the component test meter of the Vantage Pro over the various we use the troubleshooter in the scan tool we go to mental we read about description operation we go on the internet google it magneto resistive ABS wheel speed sensors and I have to tell you another place that I use ia TN again type it in under the search box and the forums and what you will find is discussions on these two different types of magneto resistive ABS wheel speed sensors it is in there right this is where we do homework we can also do our own homework don't you think we have a working wheel let's do some tests on this working wheel and see what we come up with I showed you a couple of these pictures already this is with the wheel not turning this is with the wheel turning so one of the first things that we did is we tried to look at this signal now here's the thing we know this is the signal now don't we this is the working wheel this is the right rear the right rear has a signal and a ground guys that separate wire you know the wire that's lit all the time our test lights lit it's a ground water it's not a signal we know this I'll show you why as we go so I have this signal here and what we did next is I want to see a little bit more detail in here and so what I did is I a see couple dis scope so on the Vantage Pro what we would do is we would come over here to this box and we would select that box right there and channel one and then we come up here and we checkmark AC coupling when you AC couple a scope it will block all DC constant what was my DC constant in this DC cost that was ten and a half volts right and that voltage is changing in some of these pictures because battery voltage is dropping but so what's ten and a half volts going to look like on an AC coupled scope it's going to look like this we have a flatline flatline zero volts now now why would I want to do that what that allows me to do is to take this area you see those small changes we said it's around 400 to 500 millivolts is what we're looking at on a min/max on that one it's about 500 millivolts on that cap sir in the one previous this one here this is this is around 400 millivolts on this one it allows me to take this and lower it what did I do what did i do right there I lowered the scale on the other one I was on a 20 volt it's kind of hard to look at 400 millivolt changes on a 20 volt scale don't you think so if we AC couple it drop it to a 1 volt spin the wheel this is what that same signal look like we have a min max you can see up top up here 0.297 point 2 4 2 so around 500 millivolts peak to peak on this square wave it's got a lot of noise and a lot of Hafs but remember this is a very very small signal and I'm probably peak detecting this which I shouldn't be which is our sample rate so the next picture I filtered it checkmark filter and then I grabbed that picture again in a filtered mode right there questions on how I got that signal to look like that I think that's a lot more clear than what we were looking at I don't know if it's completely necessary but I wanted to see something substantial you guys I spun that wheel when we see that supply voltage only changing by 400 millivolts current flow can do that on a circuit our signal wire which was supposed to be 0.8 - 1.8 we weren't reading that we're reading a flat line 0 this is the only signal signal we could get out of that right rear so we did all these texts on the left rear and what we called was a bad speed sensor we were able to make that call because of the right rear and the readings we have fixed low voltage on one wire look like a ground to us test light lid on it connected to that sensor voltage zero on this one fixed at ten point five on this one again test light connected to battery positive on that wire it lit brightly according to the float art that's short to ground on that wire it did that on the right rear to on the working circuit okay so it's not a short to ground we know the float arts wrong actually we didn't use the float art until after we were done I'm just showing you another bad float or truthfully we called the left-rear speech that's weird enough info and then after we replace the left rear sensor the rest of these pictures come from that left rear and what I want to show you is some other characteristics of this that we can apply to future vehicles okay first capture because I read some information guys on current flow and I believe initially I read this from a different vehicle on Mitchell and then I read some articles I believe on I Etienne and it was talking about amperage remember we couldn't measure amperage before while I was using an inductive ammeter and it was too small of an amp it's to see on an on the inductive a meters that I have it doesn't matter which one I have try measuring seven to fourteen billions that's what we're looking at in this cap sir this picture to the right this is 14 milliamps let me give you a decimal that'd be point zero 1/4 of an amp point zero zero seven we're going to monitor seven to fourteen million so how did we get this picture here's what we did we took the sensor we took the connector separated it so this would be the harness here this the cab is up in this area the wheel speed sensors down here and what we did is we installed a jumper wire on this side and we installed our in series and meter on this up so you guys understand how I got this picture to the right right here on the Vantage probe actually to Vantage pros here you might be thinking why am I using two Vantage pros you cannot when you use the internal amp meter sorry when you use the internal ammeter say that correctly on a Vantage you cannot monitor voltage on another channel because you're connecting that comport to something else you can't do it once you're using the ammeter you're limited to single channel so if I wanted to show you both voltage and current at the same time I had to grab two different tools to do questions all my connections here you guys understand where I'm measuring my current in this picture to the right okay current to the right voltage to the left I need to talk about this voltage again and really what brought this to light was the fact that our battery voltage was dropping throughout the day so these these numbers if my battery was towards better would be higher let's be clear on that this 10 point 0 2 volts would be higher if the system voltage was high okay turn the wheel just a hair got one of this teeth to move on the tone ring what do we see now 7 milliamps and ten point three volts that makes sense at 7 milliamps we would have less of a voltage drop at 14 million we have a little bit more of a voltage drop suits 10 point Oh to ten point three that makes sense this is what we're seeing this is our amperage change on the sensor so the material that we read about these that they draw or change a digital signal from 7 milliamps to 40 milliamps is accurate what's why am i reading this on I am reading this on my supply voltage wire which we now know is more than just the supply voltage it is the signal now I took this a little bit further for those of you that are curious and what I did spawn the wheel show you the on/off square wave to the right that's amperage and this on/off square wave is actually here to the left our voltage just hard to see because it's only a 400 to 500 millivolt change next thing I did is I wanted to show you that ground wire that we weren't really totally convinced was the ground this is it right here so I took that that same picture but I did it differently now we put the jumper on this side this was my supply side okay my supply and we put the ammeter on this side now if something else I forgot to say in the last segment the side that my ammeter is on is also the side that my voltmeter is on so this voltmeter was on the other side with the ammeter previous okay so monitoring voltage and current on the ground wire now previously I was monitoring voltage and current on the supply side at the same time what do we see seven milliamps on the ground and we see zero volts on that ground remember current flow what comes into the sensor is leaving the sensor we have the same seven to 14 million signal on this ground water notice zero volts on the voltmeter what do we have 14 million seven million spin the wheel don't have that picture sensor connected this is connected to that speed sensor this is going to the cap we have that seven to 14 million signal oscillation coming this way and we have the same seven to fourteen million and bridge coming the other way this is a ground this is a ground and this is our supply / signal on this call could they be monitoring amperage on the ground wire on this circuit I guess they could be and then if that was the case you could call it a signal but this is a ground in every other circuit that I would work on so completely different design last picture I'm showing the same AC coupled signal this is my supply wire AC couple to the left here and amperage at the same time so now you take your pick on how you would want to check these circuits to sum this up oh there it is this is with the wheel spinning on the ground wire for the sensor you see we have amperage to the right no voltage to the left last shot wheel spinning on the signal wire showing amperage to the right and the signal to the left AC coupled so we can see that min max voltage looks like about 600 millivolts in that capture point 3 negative 0.316 positive 0.3 0 1 these were our makeshift connectors we took the old speed sensor connector cut it plugged it into here strip the wires there down here you can't see them and we connected that was how we connected our our circuits thank you Scott should be saying Scott in all of this this is how Scott connected to the circuits this was our makeshift connections kind of crazy looking to do all this I wouldn't do it in the future checking one of these I think here's how I would handle this guys forget about the amperage I don't care go back to the beginning checking one of these in the future this is how I'm going to handle it number one I'm not going to connect an in series and meter to the sensor I don't see value in it okay so it measures the amperage - I don't see value in that because an amperage change should have what a voltage change can we monitor voltage on these circuits and condemn them monitoring voltage alone and I believe the answer is yes and it's real simple measure your supply which we know is our signal on this one right spin the wheel what should we see somewhere between 400 and 600 millivolt change as we're turning the wheel that's not much is it you better make sure you have a good ground on your meter could we say 300 to 600 millivolts somewhere in that range we should have an on-off signal do we need to AC couple the scope to see it no I really don't can you see the signal in here you can next thing you would want to do is to check your ground wire what should it be steady voltage on that ground water with it plugged in spin the wheel make sure it's low voltage all the time - something I'm pretty sure this is what it would look like with a bad ground an open ground at the sensor itself we have our supply and our ground if we have say 10 point 5 volts coming in if this ground is open between this wheel speed sensor and the cab if this ground is open right here you are going to have I don't want to say it's ten and a half volts because this is a solid-state device and I don't know exactly what we'll have on this ground wire would you agree with me though that this ground voltage will be high in this location if it's open right there every other circuit that you give a power to and take ground away you will have high voltage on the ground so how do we recognize the ground on this real simple you take your voltage reading compared to ground what do you want to see near zero volts come up here on this supply / signal wire measure int if it is a steady unchanging voltage what do we need sensor sensors bad should we maybe eyeball the tone ring pull the wheel take a look make sure it's attached with a cracked tone ring give us a no signal one on this sensor the answer is none we would have a signal but it would be erratic one of these square waves would have a frequency shift so if that was the case okay as I'm talking about this is there a time that we may want to AC couple this to see some better detail this was just a time-based change this is a one-second time base and this is 100 millisecond time base is there a time where we we may want to AC couplet so we can see a glitch in one of those and I think the answer is yes AC cop would throw a filter in there look for what would this look like with a cracked tone ring you would have one of these signals would be missing or the gaps between two would all of a sudden shift on you that's what it would look like do you guys understand the difference in this one compared to the 2006 Colorado that we just did I mean it's I don't want to say it's night day different but your approach is different is one more let's compare the two this is my 2006 Colorado and this is my this is my 2008 Jeep both of these what do we have when we started we had a supply voltage of around let's call it ten and a half volts for both of them I think we may have been a little bit higher on the Colorado because our battery voltage was higher and I believe this 2008 jeep would have higher voltage here if our battery voltage was was better on both of these vehicles we had a 10 and 0 when we started yet we approach them differently now we have two on the Colorado this 2006 up top what we did we monitored a known good one what we should have down here is a Z naught 0 0.8 to 1.8 square wave on the signal is what we should have on this wire right here this is the signal wire on this design this is the supply on this design we should have a square wave we didn't knowing that this was a pull up design a week we made that determination by unplugging a known good sensor in this stayed at zero so we knew that the way the flow was in the circuit that the sensor this is my wheel speed sensor here generates that square wave and sends it on this lawn in that direction what did we do in that video what did we do on that car we took an LED test light connected to battery positive we touched on and off that wire while we monitored the scan toll uh and that was the left front wheel speed sensor signal and what we saw was a mile per hour increase when we tapped on that water why did we do that on this design what was our concern our concern with this is that we have a short to ground in that wire that's pulling this to zero all the time that was our concern and we addressed that by doing the bypass test what did that allow us to avoid it allowed us to avoid disconnecting the cab and disconnecting the speed sensor and monitoring the circuit for a short to ground with an ohm meter saved us a bunch of time it also made us very very comfortable with the computer and how it was going to react so on the top design check your supply check your signal signal fixed at zero unplug the sensor get it out of the picture do your bypass test that's what we did in my 2004 video Chrysler I used an incandescent test line I think after looking at that manufacture flow chart I'm a lot more comfortable with the incandescent test light is that going to be a little bit too high a voltage on that circuit yes I believe the circuitry can handle it I don't think it's going to be a problem I suggest the LED test light for this it was a lot lower voltage I like that a lot better bottom picture the Jeep how do we handle each vehicle comes in ten and a half volts zero on the common what we think is the signal it's not a signal though okay there is no need on this design to do any bypass test in fact when you do it you'll disconnect this and try the bypass test you're not going to hurt anything we know this for a couple reasons one the manufacturers telling you to do this to check for a short to ground right they never told you to unplug the cab doing that disconnect the sensor test light battery positive touch the quote signal wire which we know it's not this is the supplied on this design and we're saying this is also the signal and we're saying that this is the ground so what happens down here when you try to do that bypass test you connect your scan tool we're looking at this this left rear sensor in this case it stays at zero the whole time you're doing this test on off on off no change test light lights so you use an LED test lights so now you think well maybe that's not enough so you use an incandescent light it's the same thing it likes really bright doesn't work you're thinking short to ground you have to remember the jeep design on this design there's really no need to do a bypass test and here's why this is a ground check your ground it should be near zero volts we use the same spec we use for all of our other low voltage or low amperage sensor circuit say less than 100 millivolts is a good number on that ground check your supply if your supply is good on this design do you need to go any further is there a need to do any bypass type testing and I'm saying no and I would really call this is probably not accurate but for my my mental thought process this bottom design I would call this a pulldown design can you understand why I would call it that the computer is sourcing the supply / signal circuit and this thing is manipulating it partially not fully to ground I am definitely wrong about how that actually works but in my mind that is good enough to troubleshoot this circuit check your supply voltage which is your signal voltage if it's there you're done put a sensor in it do you understand there's no need for the bypass test in the bottom picture where the top picture there was because we could have an a short to ground in that signal that were not identifying what would have sort the ground in our signal do on this bottom picture it would pull your supply damp down to ground which is your signal so what the ground is not a concern maybe top picture you think and open okay if you had an open in this wire what do you think your voltage would be here it would not be zero I promise you that we would have some elevated voltage on that probably a lot higher than 1.8 it might even be as high as 10 and a half if you go to one of these sensors and see 10 and 1/2 on both wires you have an open in that circuit fix it bypassed that's not needed you already know what your problem is and opening the ground down here again elevated voltage and open in this signal or supply up here what do we have in this location zero volts we attack this like every other circuit now I just think that it was important to go over this with you guys I learned something too that we have two different types of magneto resistive speed sensors out there and there's probably more I would be surprised to see other types low amperage circuits do we need to measure the amperage I don't see a need to measure the ampere tear I showed it to you you can do it I don't see the need to measure the amperage is the voltage enough I think it is remember both of these types and of course if you forget you can always come back and watch this at a later time it'll be there for you that's the idea any questions anything what we'll do later because we're on an ABS run here it seems like I want to go over the different design variable reluctance type ABS wheel speed sensors with you guys because there's a lot of those we've been using those for the past 30 years you know these magneto resistive ones are relatively new now o4 isn't new they've been using them for a while but they don't use them across the board so I think it would be worth doing the other type with you guys too and we have a video to go with that we had one with an open and a wire using bias voltage and things like that so we'll do that next anything else on this guys guess what I would not be surprised if they start using these four cam and crank sensors too from a simple standpoint there's only two wires instead of three I believe it would be a cost-saving thing are we going to see a lot more of these I believe yes we're going to is it critical that we know how they operate it is it also changes some things for us too one of the things I have always said for revolution type sensors something measuring rotational speed ABS axial transmission output shaft input shafts camshaft crankshaft signals when you see a two-wire sensor it will be an AC sine wave it creates its own voltage when you see a three-wire sensor it's a digital square wave it's a Hall effect guess what's now changing that looking at wiring identifying the sensor is now changing agreed this to wire abs will speed sensor that we're just went over is not is not a AC signal to digital completely different look for it I think it's coming I really do I think we'll see this a lot more I don't know I'm not the engineer but I think if you can save one wire on every single car there'd be multiple wires right that's a lot of copper if you think about it from a manufacturer standpoint I think you'll see a lot more I don't I don't know that for sure but look for

Channel: ScannerDanner

Views: 51,574

Rating: 4.8759122 out of 5

Keywords: digital wheel speed sensor, training, ABS wheel speed sensor test, how to, auto repair, car repair, Jeep Commander ABS, WSS, magneto resistance sensor, technician, scannerdanner, ABS light, ABS

Id: LKJWkAGMOfQ

Length: 58min 19sec (3499 seconds)

Published: Sat Nov 02 2013