all right welcome back so we’re going to go ahead and look at some math signals and how to do some probing on this car this of course my Trans Am and we can see right off the bat that we have a lot of homology with what we just learned so zooming in we can see what is clearly an intake air temperature sensor this is the MAF sensor this is actually an aftermarket math with a larger diameter to match the larger diameter intake manifold as some modifications I did and will talk a little bit about performance with these things in the third part of the series but let’s go ahead and take a closer look at the wiring on this map and we can see from the wiring on this map there are three wires so without needing a wiring diagram without having to consult a manual without having to rely on some fancy verus or whatever that would cheat and tell you what these wires are we should be able to pretty easily figure out what these wires are very quickly because we now understand the operation of the sensor and incidentally these are this is an aftermarket pattern if we look here if we look here this is the original harness connector and we can see we’ve got a red a black and a yellow and again I do not know I’ve actually never done this before but I am going to guess as I hope you would that the red wire is probably going to be the 12-volt power the black wire probably ground and the yellow wire probably a five volt reference wouldn’t you think so let’s just go ahead and before we break out a scan tool or anything like that let’s just go ahead and verify that all right real quick disclaimer as a result of all the idiots that have fried their PCM is trying to do this when they didn’t understand the material this is definitely one of those cases where if you don’t know what you’re doing you can destroy the PCM especially because we’re dealing with a 12-volt source here if you send that 12 volt source directly to the ground then pretty much either way you look at it if that 12-volt source is coming from the PCM and you put it directly to the ground without the wire the math wire in between you’re going to fry that PCM conversely if the ground is controlled by the computer and the computer is grounding it and you put the 12-volt by accident right to that ground you’re going to destroy that computer so a lot of people have asked me to do a video on how to not blow up your computer there is no such thing understanding the circuit design and understanding the PCM control is integral to knowing how to not fry your PCM here so I just wanted to make that comment don’t do this unless you’re comfortable with what you’re doing alright I’m pretty sure I won’t need the engine running for this which is nice because the engines kind of loud I’m pretty sure just ignition on will have a 5 volt and even a 12 volt to the MAF at all times here so what I’m going to do let’s just disconnect this and first of all see if we were correct on our wiring guesses I am quite positive black is going to be the ground so I’m going to carefully go ahead and probe the red wire and there we see our 12 volts obviously so that is the power wire of course for the math wire itself that means this other one’s going to be 5 volt reference there and we can see 5 volts so actually we even did a little troubleshooting here even though we didn’t mean to we have verified without question that we have ground signal and power at this connector so if we do have a problem with the MAF sensor very very likely it would be the sensor in that case because we’ve got all of the components from our feed now that is not good enough we are going to have to measure signal from the SMAP sensor while it is operating and see it measure changes that is going to be a problem using this tool here because I happen to know for a fact that this is a digital MAF sensor and I’ve never probed one before I’ve used a scan tool on it a few times but I know because I did the modifications here this is a digital MAF sensor so when I start the engine if I probe that signal wire and the ground when I turn this car on that’s going to change to 2.5 volts and it’s going to stay there no matter what I do because of that on a frequency that we are going to see because it is digital so let’s go ahead and verify that and okay this thing just made a wire out of me it is definitely reading much more than

2.5 volts and let’s see if it changes well it changes slightly but not proportionately so you know there there’s only one explanation for this and that is that there’s a probably I would estimate like a ninety percent duty cycle on this yeah that that is the only explanation of what that is okay so you guys are electrical engineers are either know that I’m wrong on that which I know I am NOT or you’re saying wow you’ve come a long way in your electrical understanding Matt now yeah I promised you guys that I would dedicate more time to this other guys are asking what the hell are you talking about and then other guys are like dude dude when are you going to change a myth but let’s take a break real quick because this is important I want to explain why we saw that because this is this almost looked like it was analog and as I increased rpm we see we saw a slight drop there with the voltage that is not as exactly as it looks and I’m going to show you why that is okay sorry we’re just going to go over this real quick here but there is only one explanation for that because I am I am NOT wrong when I drew that square wave earlier it is important to notice that this distance of time remember we’re talking about time here this distance of time here is equal in my drawing to this distance of time here so this amount of time on is equal to this amount of time off and incidentally just because this is at the bottom of the scale that does not mean that it is off it is possible in some systems depending on the the control and the polarity that this is off and this is on but the point is is that this amount of time if this if up here at five volts is on this ratio time that it is on compared to the ratio of time it is off is known as the duty cycle and that is the percent of time on compared to the entire signal the entire cycle for that signal now you also are well familiar I’m sure especially because fuel injectors use this all the time of the idea of pulse width then most of you guys are aware that pulse width is the amount of time that the signal is on and at a longer pulse width there’s more fuel added because the injectors open longer you need to reduce fuel you reduce the pulse width so while a duty cycle is a percent for the time on relative to the whole cycle a pulse width is the specific amount of time in seconds usually milliseconds in an automotive application is that that signal is on so it is not a percentage it is the actual amount of time on okay so just just to make it real simple let’s make this extremely simple let’s say that here to here is only one second we’re on half the time we’re off half the time 50% duty cycle point five second pulse width so hopefully that should be clear now you do not always have a 50% duty cycle the only explanation for reading four volts like that on that car which I know for a fact is a digital signal is this the signal in this car has to have approximately an 80 percent duty cycle so it spends while it’s still a square wave and it’s still the same repeating signal over and over again it’s spending eighty percent of its time on instead of 50 percent so now again with the voltmeter taking averages it’s more likely to make a measurement of the on signal than the off signal so it is reflected because when it’s averaging it is averaging point four volts now because we have an 80 percent duty cycle here if this were a 50 percent duty cycle it would have measured 2.5 volts now admittedly when I increase the frequency we had this number drop a little bit but the drop was nowhere near the proportion of the

throttle angle and so therefore I you know maybe there was a little bit of change in the duty cycle but the point is is that it was not proportionate it was not accurate now that said there was still a change when I increase does it indicate does it indicate that at least there is some change in frequency and it most certainly does but the thing is is that it’s not a very accurate way of doing it now granted this is all conjecture here although I’m positive this is what it is the only way that I would be able to prove that this is indeed what’s happening is if I had an oscilloscope which as you guys know I don’t have wait a minute yes I do okay guys for those of you that are following the channel I know I know but a lot of you guys have asked me please do a video on MAF sensor diagnosis and the reason that I never have done one up until now is because I knew I would have to cover digital maps and I did not have the ability to do it properly and thoroughly and accurately unless I got a scope as you can see I finally got a scope and no I am surprised as well it is not a pico scope but I will do another video where I talk a little bit more about the scope that I got and everything I actually just got it yesterday I bought it used from a guy and I have a complete kit with low amp probe transducers everything I’ll talk a little bit more about that I will tell you guys were right totally worth the investment but let’s get back to work here basically for those of you that are not familiar don’t be intimidated here scope is just a very very fast multimeter we’re talking two thousand three thousand cycles per second on these frequencies no problem this thing measures like millions of times per second so very very very fast anyway like I said we’ll talk more about the scope and some of the applications later what I want to do and this one’s a little fancy I can actually choose my vehicle and this model of the scope has a ton of information that the guy told me will actually tell me what the sensor connections are and everything I first of all do not will not be using that here because I want to show how we can figure it out since most of you guys will not have that information and second of all to be honest with you did we not because of our understanding and knowledge figure out the connector pattern in like what five seconds it would be faster than if I were to scroll through all the vehicles in the whatever I’m sure it would anyway you’ll have to excuse me I’m not very familiar with this because I literally got this just last night let’s go to the lab scope I don’t think we need two channels here and let me start the car up and see if I can figure out how to get a signal on here I actually have not tried this I know what a lab scope is I know what I want to do the first thing is I think 10 volts should work there and I don’t know that should work I think that should work so we should see the square wave on here and let’s go ahead and see what it looks like okay so let’s bring that up a little more let’s see if I can figure out how to do this let’s take a closer look there there we go and you’ll have to excuse me I know some of you guys are like dude you’re doing it wrong but I’m I promise you the next time I do a video on this I’ll be much more trained on this the thing does come with an amazing amount of training stuff right on the tool so I will do my homework don’t worry but we can see that it is exactly as I said the pulse-width is is quite long on here and you can actually do things to measure the actual pulse width in milliseconds there but we can see that we have clearly an 80 or 90 percent duty cycle at least it is why notice we’ve got voltage shown up here let me go ahead and do this okay so here we can see we’ve got our traditional meter along with our scope signal notice that there is also traditional meters shown in this smaller screen up here that’s matching pretty much now when I increase the throttle watch what happens this is going to squeeze together an awful lot I imagine representing that increase in frequency but it is not going to be proportionate to the meter change so let’s try it as you can see the frequency did change

but it’s not proportionate to the voltage change there so there is a pretty good method there to test that we are getting proportionate frequency change all right and there’s all kinds of goodies I can do with that but let’s go on to something else and just because we saw the change in frequency and all that and it look proportionate it doesn’t mean that there isn’t a problem with the MAF sensor the MAF sensor may not be calibrated right so while it does have changes in the frequency the MAF sensor is still not properly measuring the amount of air we’ll talk about in the diagnosis part now let’s go over to another car real quick alright this is a math connector on another car the first thing you’ll notice is this badass wannabe has five wires it looks like one two three four five wires so based on our understanding without having to pull up a wiring diagram or god forbid go on to a freakin chatroom or forum or something based on what we know what design do we have here we know that we have a math and IAT integrated together in this unit so this presents a little bit of a problem because if we watch the IAT video we know that it also has a five volt reference so how are we going to differentiate between which is which well one way I could use my fancy tool and I’m sure it would probably tell me the second way of course lookup wiring diagram whatever or the third way we can use our brain and figure it out based on what we know so because of our high degree of understanding from all of our dedicated study we have a lot of ways that we could actually do that using our brain one way we could remove this unit put a hairdryer to it and then test for which of the wires gives us a change in resistance I actually show that in the IAT video which is in the description that would be a way of doing it another way we could do it is we know that the intake air is going to be relatively constant but the change in the mass signal and I don’t know if this is digital or analog I’m sure it’s digital we could do a test there to see if we back probe a couple of wires that we suspect are the mass signaling ground does it change when we hit throttle well the other set of wires does not change indicating we found which one is IAT which one is math all kinds of ways we could do it so um let’s do this one of the things because it’s five wires we we already know the design we know there’s going to be two wires for the IAT and three for the math okay so let’s uh let’s just go ahead and get a reading here and again I have no idea what these wires are but we’re going to figure it out one thing I think I may see here is possibly a black wire so obviously I’m going to suspect that to be ground I don’t know for sure and when I probe that we get a very low voltage right there actually kind of suspiciously low that that actually I am going to take an educated guess and say that that is the MAF sensor signal and ground now given that given that information let’s assume that to be true if that is correct and I am on the MAF sensor signal and ground what type of sensor is this is this digital or is it analog almost certainly this would be an analog because we’re close to starting at zero and we would increase with the engine speed I find it very hard to believe this is like a 2013 or something I find it very hard to believe that that would be the case but we’ll have to see if if this is the math signal we know the circuit design right off the bat just from that voltage reading either that or when we start the car it’s going to have like a ten percent duty cycle or something which isn’t going to happen but let’s keep that in mind let’s see what happens now let’s let’s move over I’m confident that this black wire here is also a ground most likely for the IAT let me check that and we’ve got two point six volts now remember the engine is not running the engine is not running right now I’m much more inclined to believe that is the IAT if the engine were running I would say that we probably have a digital map so let’s do this let’s go ahead and turn the engine on and let me make sure these wires are out of the way the belt and see what happens with that number and what happens if we change over to the other

side actually you know what better yet let’s just go ahead and leave that there put the scope on the other side and we can kill two birds with one stone but of course you could do the same thing sequentially with just the meter the the Volt that’s probably going to be small to see here so let’s go up here and use the digital multimeter it’s got this big ass meter on it but I think it’s kind of cool there if you can’t see that you got a problem and what we’re going to do is you know what actually here’s the thing let me get back into that ground there there’s one wire that we forgot to test here and that is this green and yellow right in the center what do you want to bet that that’s going to be the 12-volt power source for the Hotwire so let’s go ahead and do that might be a little hopeful okay and when I do that it well it clearly means that it’s out of range oh because we’re only on a one volt scale so we can change that twenty volts should do it okay so there’s our battery voltage obviously so that’s really cool you see how intuitive this tool is by the way I love it what we want to do now is now I want to get off of that because we know that that twelve volts is going to be constant so let me get off of that but this makes kind of engineering sense sort of that the left side is probably going to be the MAF sensor just from the order of the wiring so let me get back into what I believe is going to be the MAF signal okay there we go and let’s get back out of here I’m I got to tell you I’m pretty I don’t know for sure but I’m pretty confident we’ve got this right and this is going to be an analogue measurement let’s go here back to our I want if there’s a quicker way I can do that you guys don’t have to worry about making comments to help me out with this I’ll figure it out but if this is analog let me increase this here if this is analog we’ll know if this is digital we’ll certainly see the square wave so let’s go ahead how do i hope you guys follow what i’m doing here my I’m hoping I’m not losing you here but what I’m doing is I’m trying to find out for two things kind of simultaneously first of all which of the wires is for the math which is for the IAT I’m not interested in the IAT and second of all we don’t know the design whether this is digital or analog if we do find the math if this number doesn’t change much but we see a lot of change here with throttle then we know that we are connected up to the math here and the IAT here let’s find out all right it is pretty obvious that is going to be an IAT and that is going to be a math sensor so the one way let’s go ahead and increase the RPM unfortunately and you know what there’s no square wave here and we’re at two volts this there is no question about it this is going to be an analog signal which means I’m going to have to dramatically change my time frame here let’s put it on to maybe a couple seconds like that okay so what’s going to happen this is going to look because there’s no square wave obviously this is analog I’m amazed by that and we’re going to see when I step on the throttle the IAT of course not going to change much but that’s going to look almost like a throttle position sensor signal this is a drive-by-wire vehicle so I’m going to have to go into the vehicle to do this so you’ll get to see it before I do and actually because of that because you’re going to see it before I do I’m going to increase the time frame so I can come back and see it okay quite obviously and we can bring our scale a little better here okay quite obviously we are on the MAF sensor I’m no longer worried about this I’m just going to go ahead and get rid of it that was clearly on the that’s a pretty good guess I guess but let’s go ahead and verify if if I go wide open throttle that voltage should spike up pretty close to five and you can see it’s giving a min/max here it looks like I’m sure that is all right the engine has a rev limiter on it at a certain number so it only limits me but clearly clearly we are and that quite sure why it stopped there let’s try refreshing it but clearly we’re on a map sensor so we could we can measure this we don’t need the scope

let’s get rid of the scope because I know most you guys don’t have it let’s go ahead and hook our D vom up to it actually I take that back we do have a DV om here so this would be no different than hooking up your standard DVR going to be able to see the changes in voltage proportionate with the throttle engine speed bringing air into the MAF sensor all right and again activated the rev limiter there and clearly we you you would have seen the difference there I didn’t get to see it but I’m sure it happened okay you know what I’m going to do just to prove a point of principle here let’s go ahead and use our cheat sheet here to go ahead and pull up that that wiring pin just to make sure we were right but also to see if we can get a speed comparison whether brains can beat a computer I’m going to go to US imports the Subaru and sure it’s going to be under fuel injection but I would expect a lot more stuff there um this one of the things getting this tool used it’s only going to go up to 2007 so let’s go ahead and do that this is an outback this is a 2.5 litre outback okay yes to accept and sorry if this is boring but ok so now we’ve got to find the map I’m sorry the MAF sensor okay oh it’s got to be called something other than the MAF sensor then from Subaru so let’s see we’ve got an air fuel is not it Baro that’s going to be a map is there also a map on here I know so Baro is going to be the map you know what oh there’s the i-80 I guess we could have looked at that I do not see anything that even remotely there is no MAF sensor on here you know what that is cool and I will tell you why that is cool it is because you can imagine that you’re 98 percent IRR that just figures hey I don’t have to learn any of this stuff all I need me is one of them fancy gizmos and it just tells me what to do and I don’t even have to understand what I’m doing well guess what it didn’t have the information you needed there what are you going to do if you are a mobile mechanic and you are in the field doing a diagnosis and you’re super fancy tool didn’t have that information you can ask the customer hey you don’t happen to know how to probe a MAF sensor do you you’re stuck like Chuck man so you still even with really good equipment have to understand what you’re doing in this stuff so that you can figure your way out of situations that I am actually thrilled that that happened and as you can see even if we did have the ability to find the MAF sensor in there because of our understanding that we’ve spent time learning for the last hour we would have been able to characterize that system with our digital volt ohm meter faster than we would have done with this anyway so that that feature with components and everything not really so much a selling feature for me but anyway enough with this we’re going to use this again when we get into the diagnosis I bet so let’s get back to the dry erase board and knowledge clean up this section and then the next section of course will be diagnosis of things that can fail in a MAF sensor and how to diagnose it so close out this first section we still have two more things that we have to do for understanding the data outputs based on what we’ve learned earlier we still want to look and see if you happen to own a frequency meter like a you know higher-end DV om that has that we need to look at what that looks like on a digital MAF sensor and then finally let’s go ahead and look at if you have a scan tool what your scan tool output data would look like and make sure it matches what I said earlier since I don’t have a DV om that has frequency measurements I know I saw this in here when I was playing with this last night so again I’m just hooked up again between that signal wire and the ground wire if you have to ask hey you didn’t show what color wires you’re probing the color of the wires is insignificant we are not looking at these as black yellow green gray whatever wires we are looking at these wires by function by what is the ground what is the signal what is the power if you are still at the point after watching this video that you need to see the colors of the wires and you’re still thinking in that way I don’t know what to tell you you got a ways to go but anyway let’s see here um and it’s not there and I apologize there’s frequency

right there okay let me go ahead and I have no idea what we’re looking to do here let me go ahead and start the car and obviously we’re going to have set some scales this is completely new to me the one thing I know let’s see we want we’re surely gonna I mean 10 Hertz we’re going to be way above that yeah let’s do that and then because there’s already actually should be a frequency I think I have the car on I’ve I forgot let’s go ahead and run this and see what happens okay I am totally figuring this out as I go but looks like a pretty good guess we can see two point three three kilohertz there and it looks like I’ve got maybe two channels going or something here but let’s see and it goes up to four and a half kilohertz almost so we definitely can see a frequency change by using the frequency meter we can maybe make that a little more I think we can probably go here I don’t know that that graph helps very much but we can now you can see the it is kilohertz and one of the things that’s pretty cool is a lot of times there’ll be a specification in the service manual for your kilohertz mine’s a little bit high actually but again I believe that’s because of the modifications obviously for the engine but we should see what obviously is a very proportionate signal increase a more compression it would be of that square wave represented just from the kilohertz signal all right and our final part of this initial segment is looking at the scan tool pits that you would get so we already have an idea based on the function of the map sensor what we might expect this is on the TransAm so I don’t expect we’ll see voltage on here but let’s see what we’ve got for it here and while I look zoom in a little bit there if you told me a year ago I’d be doing a kilohertz measurement on a digital map sensor I would told you you were crazy because I wouldn’t even know what you were talking about so obviously anybody can learn to do this if you just dedicate yourself to it there’s mass flow error rate so we’ve got three things here for mass air flow that are available let’s go ahead and pick those I’m not quite sure what mass air flow sensor one is the rate is guaranteed that’s going to be on this car in pounds per minute the frequency it’s going to show as we saw before I’m not sure what this third one is though okay and the third one is apparently pretty much some type of extrapolation off the first one that maybe with without IAT possibly I really don’t know notice our Hertz is pretty much what we found using the Hertz meter so if you did not own a Hertz meter scam tool would work and vice versa and that’s pretty much all the data we have increases proportionally with the Hertz there’s the data from the scan tool just like I said you’d find all right those of course were the kids that we got from a digital math let’s go ahead and look at this analog map that we know we have on this other car I expected we’ll see voltage so let’s see let’s clear this out and there it is mess well has this mass air flow rate what kind of a dip is that only one pit there well you know what all the more reason why you want to have a good understanding of this stuff so that you can have multiple approaches to a diagnosis all that’s going to do is just give you the same reading in a g/s there so all right disappointing all it does is give the mass airflow rate no voltage reading there or anything so that was kind of useless all right well that just goes to show that you are a lot better off having a lot of knowledge and understanding than just relying on the scan tool or whatever that was a amazingly minimal amount of data from either car actually if you think about it but anyway for this first part of this diagnosis and understanding video we have achieved our goals I hope of understanding the purpose of the MAF sensor and also the different types of MAF sensors the different types of circuit designs that are available with math sensors lots of ways to be able to assess that circuit design read the output using various methods I think we

covered a lot here so it’s time to move on to part two and that is taking that information now and learning how to make a diagnosis on a failed MAF sensor and also using the math sensor in diagnosis of other sensors so we will go ahead and we will do that on the next video but I will give you a preview here and in the next video we will cover the four possibilities you would have and how to test them for a mass sensor problem those would of course be a failure of the MAF itself some type of lack of integrity with your circuitry a inaccurate math very common one dirty man censor things like that the math being inaccurate will often not give a mouth code these would give mouth codes and your average 98% idiot is going to change the MAF sensor probably get lucky on it but how many people change the math because of lean conditions things like that that is the result here the other one is the math on a referenced code we actually saw that in my last series with the Volkswagen didn’t we so this is of course referenced is a term that I personally use for when a part is actually given a code in the computer for the check engine light but it is erroneous it is Mis coded by the PCM because of lack of communication with other sensors which brings us back to the first thing I said in this video we have to understand everything but of course we’ll get more into that into the next video with the diagnosis of problems and as far as for this one thanks for watching I hope you found this helpful we’ll see you again soon