CAN Bus Communication Explained (Part 1)

hey welcome to can bus communication now I've been contemplating this class for quite a while now but that's because I wanted to get it right I wanted to focus on a class where you could take a car with a communication issue and go through the entire process of getting it fixed there's a lot of really good canned stuff out there but what I feel it lacks or what I really never liked about a lot of it is so much of it focuses on the protocol itself the ones and zeros the binary code or it focuses on the testing right away like what is a good lab pattern look like and I don't feel like that's the steps that we take when we're actually diagnosing these things so what I did was I took notes on what I did when I was diagnosing these in the actual shop in a real world scenario and I built a class around that and this is what I came up with so here are the four topics that I'm going to cover and these topics are topics are also in order of process we have one two three and four and you can see that Network and troubleshooting is all the way down there on the bottom and it's down there for a reason not just because I think the other three are just as important or more important than the actual testing but a lot of times when we're when we're fixing these things or looking at these things will actually get to a solution before we even get out the lab scope or even get out the multimeter to test so starting with communication networks we're going to talk about the ginormous networks that we're dealing with today and how to break them down into more manageable chunks something that we can actually diagnose we're also going to talk about why we break them up and how we break them up then we're going to talk about Network topology and this is the wiring layout of the network and this is also really important because even if we're just talking about can bus there's numerous ways these things can be wired and if you don't know how something's wired then yeah it's kind of hard to test with any piece of equipment then we're going to talk about the protocols and languages and when I say protocols I mean protocols with an S because can bus has more than one protocol and there's a lot of other protocols or languages talking around can bus on the network and we need to understand all of them and or at least how to identify them in order to be successful when we're diagnosing canvas issues and once we get those three covered then we're going to talk about the actual Network testing and the troubleshooting and this is a lot of information I know that so what I did was I decided to break it up into a three-part class and for today I'm just going to cover communication networks and why I'm starting with communication networks well I think this picture Explains It All this is what a modern day Network looks like and this is a 2021 Cadillac Escalade and it's a lot to look at and if I'm being honest it's only two-thirds of the actual Network I couldn't even fit the whole thing on here I tried but it was so small it you couldn't even pick anything out and you can kind of see already why we can't just get all our equipment and start testing because it's more about where to test where are we testing then what to test on these new networks and a good way to explain that is let's think of this as like a road map you have your roadmap and you could be the best driver in the world but if you don't know where you're going you're just going to end up driving around in circles until you either one run out of gas or energy or you just get lost and quit and that's what we're finding with a lot of people trying to diagnose these networks these days they understand the protocol or they understand how to use a lab scope or how to use a Multimeter but they just don't know where to start so that's why we're starting with communication networks and what we're going to do is we're going to break them down and the easiest way to break them down is let's start from beginning and build one up from where they started and how they're constructed because if you know how something's constructed that makes it so much easier to deconstruct it essentially so let's start with what did we have before we had networks well we had stuff like this now this could be your dad's old IROC or it could be an old Ford truck it really doesn't matter but what we had was a lot of redundancies so this is a picture of coolant temp sensor and the engine control module needed it so it could control fuel makes sense right well the engine or the instrument panel cluster also needed the engine coolant temperature sensor so it could display it on the dash and this worked fine I mean sometimes we replace the wrong sensor sometimes we diagnose the wrong sensor but whatever butt ass cars got a little bit newer then we started getting evap systems now the engine control module needs the fuel level sensor well obviously the gauge needs it because we don't want to run the car out of gas and we got VVT systems so now the engine control module needs the uh oil pressure sender and then we have that on the dash so we started getting to the point where we needed modules to have some type of ability to communicate or share information and we also got to the point in technology or advancements where they could do that so this is a solution you can see in this picture now we have our coolant temp sensor and it's sending its signal to the engine control module but instead of having another coolant temp sensor now we're just sharing information we're sharing information on the network because that's what we just created this is a simple network two modules sharing information here's an example I was just a simple Network it's just modules talking to each other sharing data and it doesn't have to be four modules it could be three modules it could be two modules but this is a network in its simplest form but nowadays they don't just share information they also work together to create systems so some of the earliest systems I can remember is the ABS module teaming up with the powertrain control module and it created traction control systems so now when you're in that parking lot you're you're doing donuts and making a big smoke cloud the ABS modules tells the PCM hey tires are spinning so the PCM takes away your throttle and you got to find the button to turn it off I'm just kidding but then we have our old radar systems that were just the beep beep beep now they're working with the big screen TVs and the cameras and now they're creating park assist and this wasn't too bad I mean it makes sense and it doesn't really change how we diagnose we just have to understand how they work together and it gets even a little more complicated than it is now we have all four of those modules and they created one of the first systems so now we have our our radar module here and it sees a pedestrian and before all it would do is tell the driver hey bbbb you're gonna hit something but now on cars it tells the ABS module to pump the brakes and it stops the car for you and if your brakes aren't strong enough because your engine's too strong then it will talk to the engine control module and it'll take your throttle away and it all it is is four separate systems talking to each other working together and this is what a communication network is at least this is what it looks like when I draw it with pictures but what we're normally going to be looking at is we're going to be looking at wiring diagrams and this is what we have to break down so let's look at it from the earliest wiring diagrams now this is beautiful this is what I started looking at when I first started working on cars simple networks like this and we had our DLC here but you know it may have actually been an aldl for those of you who remember or maybe a diagnostic port but it was just simple one-wire networks and some of these still exist but this was the whole network it was the PCM talking to maybe one or two other modules and abs was you know if you had the option you had ABS that was actually an option back then and it was just one wire so there's really nothing to break down here so we didn't really worry about it too much but that didn't last too long did it we very very quickly we got into stuff like this and this is a more modern Network that we have today not the most modern network but this is just a simple picture of what it might look like and now you can see you have three separate networks within one big Network and the thing about all these networks is not only are they all communicating at different speeds and different voltages and things like that they're also all still communicating together and now we have things like Gateway modules now if you think about it like languages let's say this red network is speaking one language this yet green network is speaking some language and this blue network is speaking some language well the Gateway module is The Interpreter that lets all these languages talk to each other so that it creates one big Network so essentially now this is broken down from a big Network to three smaller networks so this is how we have to diagnose it and it gets even more complicated and that when you look at it like this and you're thinking this is can bus communication does this really matter well when you're looking at this this one right here well this is can bus and guess what this is can bus too so now when we're diagnosing canned we're not just diagnosing one can anymore so we have to know which can we're diagnosing what network do we have to find and this you know this could be a low speed can and all three of these networks might speak at different voltages in different languages and different speeds but before we get that far we have to figure out what network we're looking at and what else do you notice about this let me get my uh John Madden stuff out of the way here look at this DLC it's not connected to any networks anymore it's connected right to that Gateway module so if we test from the DLC are we going to test any of these networks anymore no if we take our multimeter and we do our old uh true test of powering down the network that's what we always do on can right we'd power down the network we take our multimeter on Resistance and we would go to the DLC we measure at 6 and 14 and we'd look for 60 ohms can we do this anymore no we can't can we get our scope out and look for a pattern here anymore no because we're only going to the Gateway module so what's the first step we have to do we have to break this thing down what network are we looking at this can Network this scan Network or maybe this low speed can Network then we have to find out where do we diagnose it where do we tap into it where can we actually get a reading to test it and that's exactly what I'm trying to explain in this class today and this is simple remember this is what we're looking at now I mean that's crazy I I tried to count I believe there's 80 modules on here and remember there's only two thirds of it so there might be a hundred modules on this car but we can't let that intimidate us this is the first step to winning and the first step of failing I guess I would say so when you get a communication issue we need to break it down and there's a lot of different ways to do that and one of the easiest ways to do that is just like this a lot of the service information has the data networks like this so now it's already broken down in different figures different sections but it's still a lot to look at and it goes again why we can't just go right at can look at this look at all these cans one can one can two can three five eight powertrain info I mean you'll go nuts trying to look at this all at once so we have to break it down we have to look at the network in sections to be successful and let's look at a case study we'll break one down and it'll make more sense so this is a 2021 Cadillac Escalade hence why pick that initial diagram and quick backstory on this is it was at another shop and it was the fuel pump driver modules are placed I mean Chevy's never had any problem with fuel pump driver modules yeah and there's still no communication the technician that looked at it is a technician that has some can experience but not new can experience and he said the scope pattern looked good from the DLC and there's kind of a weird resistance reading but all the other modules communicate so he there's there can't be anything wrong with the network right so we look at the car and it has a DTC u18a2 yeah there's numbers and dtcs now too that's always fun so here's the code it has and we confirmed there's no communication with the fuel pump control module so where do we start well let's start by looking at a wiring diagram because that's where we always start and luckily this wiring diagram is interactive the the one I'm showing you is a little easier than you may have to go through but it's really good for learning so this is why we're using this one but the first thing we do is we check to make sure there's power and ground I mean that's the first thing you're going to do when you're diagnosing these networks but you got to check to make sure it's power on ground and there is so what do we do we have no communication let's look at the network let's break it down so what do we find the communication lines right here and it says data Community data communication schematics and if I click on that it brings me right here whoa that's only one that's not bad right and remember I said it's not always going to be this easy sometimes you have to look at each one to try to find where they're going but we still need to break them down now look what we had before we had 24 cans or 24 so now we can cross all this stuff out and we only need to look here we're already making this big thing we're making it smaller because this is the only thing we need to look at because this is where this module is going we had this before we get nothing out of that now we have this and depending on manufacture or I should say depending on option codes so this thing is showing some diesel options and you can see these RPO codes here this car doesn't have diesel cool so now we can get rid of this let me get rid of this and get rid of this and see we're not testing anything yet we're just looking at the wiring diagrams or finding the one section we have to test we're not worried about what's at the DLC we're not worried about what our lab scope says yet so we get rid of the diesel stuff and now we have this now this is beautiful this isn't look intimidating at all and this isn't and it shouldn't be but what is this missing what are we used to seeing when we diagnose can well I'll tell you what we're used to seeing where's the DLC I mean this is what we're used to dealing with can this is what we're used to diagnosing and this is how a lot of the classes kind of depicted still and it's just not going to get you anywhere we used to have the the DLC here and 6 and 14 went right to the high-speed can bus so we'd go there and we test well this is what the DLC looks like on this car if we test here are we going to get anything all of these wires are going to a Serial Gateway module every single wire at the DLC so if we test the canned circuit on our lab scope we might get a good signal right and if we do a resistance measurement for our resistors look at there's little resistors in here so maybe we'll get a good signal that's even worse than getting a bat signal because now we're confused and that's why this car ended up by us let's look at what it looks like in a simpler form we have our DLC this is what we're communicating with it and it's going right to this Gateway module and it talks to the engine control module through these modules are through these communication lines now if we test from here are we testing any of this network which we may have a problem on no we're nowhere near it this is why we can't test from the DLC anymore it's going to get us in trouble now is there some cars you can yes but what do you do first we break down the network so what else do you notice about this and this can really confuse people this really can confuse people the text said that all of these modules could still communicate so there can't be I mean if this network is down these modules there's no way they're going to communicate so it can't be the scope pattern looks good they're not communicating the network must be okay right well let's look at it again if this network's down these modules are not communicating with each other if you're communicating here with your scan tool can you communicate with these modules yeah you're communicating on this green Network so what I'm trying to hammer home is three points one we need to break this stuff down before we test two just because we can communicate with a module doesn't mean it has a communication issue think about it like your cell phone your cell phone has text and data or text and calling and messenger and so you can lose one and you can still communicate that's exactly how these modules are look at it like a wiring diagram look at these serial data lines there's a bunch of them it's communicating this is the gear shift module so if it's if this is down and we're communicating communicating it through here yeah we can still communicate with it let's look at the engine control module it's on this can bus line this can bus line this can bus line so you can see if we have a problem let's say the engine control module is not communicating with what on What lion we need to look at these break it down I mean sometimes you might even have to print out paper and use your highlighter but it's if you spend 45 minutes doing that and less time with this you will be more successful I guarantee you because this is just impossible this is why this is Step number one is speed rate or data or all the canned protocol information can help you fix a car when you're looking at this no that last car was fixed with a visual inspection once we knew that these were the four lines and these were these were the modules I communicated a simple visual inspection showed some mice chewed some wires underneath it so we never even looked at anything with this and the person before said it was good it's it's it's super simple it's like glorified map Reading I know it is but this is why we're training with this first to show you how simple it is and how you can be successful doing it and if you're thinking you know what I don't want to do this network stuff I'll just leave it to the network guy I'll stick to my powertrain performance look what I found when I was looking at these wiring diagrams and I didn't even know this existed this is the first time I've ever seen this look what I had highlighted before it's a mass airflow sensor the mass airflow sensor signal is going to the engine control module with Lin bus now that's on communication lines engine cooling fan communication line engine coolant flow valve communication line so we're not going to just be breaking these communication networks down for communication problems now we got to break them down for sensors and stuff too step one and if you want to make fun of that escalator being so complicated take a look at the BMW I know it's glorified mapping but this is 75 percent of can bus diagnosis if you do this you will be successful so we know we need to divide these networks up who and they're divided into sections but let's talk about how they're divided into sections and why they're divided into sections and we have to answer this question because I always get it okay we have all these modules we have all of these different cans why do they have to be that many cans I mean that's just more confusing wouldn't it be less confusing if there was one can with all the modules on it well let's take a peek at what that looks like this is what a network looks like when it's all on one bus and networks used to be like this for a while and Not only was it harder to diagnose but what do you see here I mean yeah it kind of looks like you know a card game but it looks like a house of cards to me modules or communication should say there's two ways communication fails either the module has an issue or there's a wiring issue now let's say this module has an issue there's two things modules do these are short short out or they talk too much now this module shorts out guess what it's going to do it's going to take down the whole network now you lose everything or if this module won't stop talking it's going to take down the whole network and we lose everything you can see it's like a house of cards or let's say wiring wise let's say this is shorted to ground right here we just lost the whole network let's say this is shorter to power now we lost the whole network and you can see why they're they're sectioning this stuff off it makes sense and also let's say we have an issue here if let's say this module is bad it's shorted out how do we find that well now we have to go through every single Network or every single module just to find out which one's bad all this wiring when if it was sectioned off it'd be much easier let's think of some real world examples and this is stuff that I've actually seen let's say this is your uh this is your driver's window switch and this is your PCM that runs your engine I say you're on your way to McDonald's and you're you're getting a cup of coffee before work and the guy who hands it to you he's got it over full you squeeze it too hard and you pour coffee all over your window switch shorts it out well now your car just died in the in the parking lot or in the drive-through and now you got to get it towed now this one might be easy to diagnose because you know what you did but it creates a system that's not very fault tolerant and it's not very easy to diagnose so splitting this stuff off I'm trying to explain that this is actually a good thing now let's look at it let's just say that this is your PCM or whatever and let's say this is the media center in in your back and your kids are back there and they're watching Paw Patrol and uh maybe they're watching a DVD and while you're on your way to vacation and you think they're just watching what they're really doing is finding all the change you dropped and they're finding it playing a game how much change can fit in that slot before it's full because that's a fun game and it shorts out the entire network so let's look at how we have it sectioned off here's your window switch you spill something on that you only lose this network your car still runs your safety systems still work and now we only have to diagnose this section of it or let's say here's your little media player that has change in it and it shorts that out now it only shorts off this section now we still have everything else and now we just got to sing our way to Vacation instead of playing the video games in the back like they do nowadays it's not so bad we did it before still get a case study and this case study is great because it shows you the House of Cards example and it shows you a tricky thing that uh manufacturers are doing to save themselves and it also shows you how it makes it easier to diagnose at the same time so this is a 2013 GMC Acadia it's got a no star condition and this was an actual car that I had the other symptoms I'll talk about in a second but it had a no start problem and it was very intermittent the customer brings it in he goes every once in a while I turn the key nothing happens like okay so I get the car in doesn't happen I turn the key thousand times the battery's about to go dead I'm like I can't see the problem I'm like is there anything else on there that you know any of their symptoms and he goes well the interior lights go out once in a while the dash goes blank and I have a service object detection message on the dash all the time I'm like okay he's like but I don't I don't really care about that I don't need service object detection or object detection it's just the rear little things in your bumper that are like radars so for any ways I or for just because I go when I look at codes and this is what I have for codes HVAC radio telematic driver's door door control remote function rear gate who cares right this doesn't have anything to do with running the car and if you've ever worked on these older GMS a lot of them come with these codes stored from the factory and they never do anything and I didn't really care I dropped the ball on this one so he didn't care about his other symptoms so I sent him down the road and guess what happens about a week later the thing comes back on a tow truck crap but now I can fix it so it comes in doesn't start just like you said you turn the key nothing happens so I get my scan tool on there this same codes are in there nothing else that doesn't help but what I do know is the PCM is not commanding the starter on I look around and I didn't see that first and I couldn't figure out what was wrong all the wiring seem fine I think it's time we look at this network problem so what do I do I look at the network and I look at it as a whole at first just so I can break it up and looking at it here I mean it may take a little while but the color coding stuff is really nice all this green stuff is one network and this will be our low speed Network and then we have all these gold ones and this is our high speed Network so looking at the High Speed network I see that we have the engine control module and the transmission control module the body control module so I'm thinking this is a network that may have a problem because I don't know what all those communication codes I don't know what network that stuff's on yet so I look at the High Speed network and there's there's all my money right there the engine control module blah blah blah but they're all communicating and I don't have any codes for that stuff I do have the body control module that's setting the codes that's where those codes came from the body control module but I don't really see my problem yet so I moved to the other side of the network to break it down now I'm on the low side but look what I see here this looks like that that that house of cards that I had before this is definitely that house of cards I had before all these modules on one line so I start going through and I start checking the modules I had codes on for and there they are all the modules that I have in Gold here are yellow those are the modules have codes for and what I also realize is I don't have communication with anything on this network so this whole Network's down someone knocked over the house of cards so this is a problem this is what I have to fix but why doesn't the thing not start well reading through it I figured it out pretty quickly the stuff to turn modules on the low speed Network the theft deterrent module is a module that reads the key so without reading the key the PCM says I'm not starting the car but look the body control modules on there too how did I talk to the body control module remember what we talked about before the body control module speaks two different languages it's one language is out but the one I'm talking to with the scan tool speaking a different language why else is this so good think about that house of cards if you take one module out you take out the whole network if we have separate modules and a module that can speak to all the networks we have a tattletail module a module that can set codes when one of them or the networks goes out remember this is a good thing we just got to break it down and here's a picture of the BCM you can see here's the data here's more data here's a wiring diagram picture over here you can see we have the low speed Network and the high speed Network so all I got to do is figure out why the low speed Network's out and this one was kind of hard because it was a house of cards but I go back to my symptoms and remember this is another thing if you can break down these networks into smaller sections think of the symptoms that are caused what symptoms does each module cause or what represent what could represent what well what was the one constant that we had that service object detection message was on that was the one thing that was always there so I'm thinking it can't hurt at this point there's a lot of stuff on that house of cards why don't I go here first this was this is the one thing that was always broken and if I look at it on a communication diagram here it is it's on a low speed Network here's the right one talking to the left one and then the left one talking to the the low speed Network and I got lucky I got really lucky it's not always going to be this lucky but here's what I found this module had water in it right here and all full of mud and then I took the connector off and there was green fuzzy stuff and some greasy stuff in there and as soon as I disconnected it I heard all the lights and stuff come back on the dash second uh or the low class small Network went back and the car started up just fine I knew what my problem was and a little more backstory is if anyone hasn't worked on GM's every single month from here on out I found more and more of these this was a major issue that GM had they built a house of cars that they didn't break up luckily this one was easy to diagnose but here's where this gets really interesting and I think you're really going to like this this is this is kind of funny kind of not funny a couple months ago and this is what really sparked this class and sparked the beginning of this class remember all the stuff we've diagnosed so far we haven't even taken out of lab scope yet we haven't took out a multimeter we've just been looking at wiring 2017 GMC Acadia so same car couple years newer it pulls into the shop it's got this object detection message but it's got a front camera message too but it's got more it's got more options so I don't really care but here's my here's my big money right here I've seen this 20 30 times before I'm gonna diagnose in five seconds but there's no other symptoms present well maybe it didn't short out that way maybe it's not showing the whole thing out but it's still kind of interesting to me but either way I put my scan tool on it and it's one of the newer scan tools to show us topography it breaks the network down for you or at least it does a decent job of breaking it down they're not perfect but they do help a lot so what do we got here we have our stuff in red and that's saying this code set but what do we really notice here what do we have down here we didn't have that before and this is the left side object detection module right side object detection module front camera module well that's interesting here's the wiring diagram we had for the first couple years of this car here's our object detection modules here's our house of cards and GM had a problem with these and they tried to fix it they started out by telling you to put some grease in the connector dielectric that'll solve it didn't solve it then they had a updated module they put a sticker over the vent hole the module to stop water from getting in there did it help no it didn't help so what do we have now for wiring that doesn't look like as much of a house of cards does it half the modules are missing and if you look here it looks like the body control module even isolates the class 2 in half and where's the other object detection module well it's right here they don't even talk on the same network that this one's talking on now they talk on a separate Network so if this one goes down it doesn't even pull the class 2 or the the low speed down and we didn't have that no star concern that we had before because look at the immobilizer now it's on its own separate Network so they fixed their problem didn't they by breaking down the network by sectioning things off and as much as you don't like it it's great for us it makes diagnosing this easier and this is why this is number one step because if I would have just went at this with the old stuff or my old thinking it wouldn't have worked because things are constantly changing let's go back to this here's our house of cards this is what they had and this is what they did they took it out what would you rather do diagnose this whole thing as one big Network or let's say this is five separate networks all we have to do is know where we're testing and why we're testing and this is the first step when it comes to diagnosing this can and I know I've said it before and I'll say it again this is just this is glorified map reading this is just investigating this isn't taking tools this isn't anything crazy but this is the this is 70 of fixing can and if you if you do this if you use this I guarantee you will be successful now I hope you liked what you see here today and if you did please hit that subscribe button hit that Bell icon and then you'll get notified when part two of this class comes out that's we're going to start talking about the protocols and the way these things are wired and we're going to get a little more depth into the can bus stuff so as always thanks for watching again I hope you liked what you've seen here today this is Ryan with gotek signing out

Channel: GoTech

Views: 221,502

Keywords: CAN Bus, CAN Bus Communication, No Communication, U codes, U1000, U1001, communication networks, Low speed CAN, High Speed CAN, Scanner will not communicate, CAN Bus Protocol, DLC pins 6 14

Id: YbF3idCk4EQ

Length: 33min 44sec (2024 seconds)

Published: Thu May 18 2023