5 Tips For CAN Bus Diagnostics | Mechanic Mindset

so canvas can be really tricky to diagnose and if you follow these five steps it should make it a lot easier now the single biggest thing that i get requests about other than oscilloscope diagnostics is canvas diagnostics and there's really quite a running theme it's either people don't quite understand how canvas works they don't understand the testing methods required to diagnose canvas and in many cases they overlook the basics so remember to give the video a like if you found it helpful and subscribe to the channel if you want to see more like this go and check out the other videos i've got on canvas diagnostics for all the equipment that we use today you can find the links in the description below so number one then is a function test and to be able to do a proper function test you need to understand how the network is connected on your vehicle and how it works so if we check out this network topology here this is um what the network looks like on my bmw e90 so we can see here we've got a number of different colors so this is the powertrain canvas so this is for your engine electronics so dme your fuel pump transmission all your power train related things and you can see there that these all come up to the jbe the junction box or also known as the gateway that's the common term for the name of this component we can also see that there's a blue one coming in here that's our chassis can on this vehicle and the red one here is that's the body cam okay so that's all your windows locks instrument cluster things like that so all of these networks we've got three can networks on this vehicle they all speak slightly different languages that's one way to think of it and what that gateway does is actually translates the messages between the networks and a really good example there is uh wheel speed so nearly every control unit on the car uses wheel speed so we can see here that we've got dsc here and that wheel speed is going to go up along this network to the gateway the gateway is then going to translate that message into a language that all these networks can understand and then you can see there that the combi is going to use it for displaying the speed on the instrument cluster we've got the radio is going to use that information for changing the volume of the sound when we get faster it's also going to use it for things like navigation we've also got the body control module that's going to use it for things like drive away locking it's going to use it for controlling the wipers at different speeds and when you stop basically goes all over the car that message so once you understand how the network operates you can perform a proper function test some of these function tests are actually really simple if we think about on this car how the turn signal indicators work so you turn the stalk on the steering column and that is actually part of this control unit here and that message then has to get over here to the frm the body control module now if there's any problems with this network then we know that that signal is not going to get there and the turn signals won't operate another thing to consider is when you turn the indicator on you've also got the display in the instrument cluster so that message has got to go from the body control module to the instrument cluster and that can only happen if the network is operating okay so the complaint on this car is that there's a multiple warning lights on the dash so abs airbag steering a few different things like that we're going to work through this together and i think you're going to be really surprised at what the problem is and how some you know some problems are are really quite overlooked quickly at the beginning so let's have a look what we've got let's um turn the ignition on okay wipers on we've got engine start fault okay i've got my foot on the brake and press the start stop button and that that should have started the car now so let's okay so straight away there's kind of alarm bells ringing that's that's something not quite all right there we've got quite a few warnings on the dash there abs steering air bag kind of related things so you know i'm possibly thinking you know something abs related possibly a network problem as i said about the function test there's quite a few things that we can do quite quickly we mentioned just turning on the direction indicator you know that can quickly check the network so if we turn that on there right okay so we can see we've got something on the dash there let's just check outside okay and that's working there as well so we've definitely got some network activity going on there right okay so if we're thinking abs wise road speed things like that and the other thing you'll notice is that the wipers are going crazy so let's just see what we've got for road speed okay so nothing okay so we've got absolutely no road speed either so okay we've done a function test there then we've got some evidence some function test results we've got the warning lights on the dash and it's always just important to remember is you know think about how this car works and how it operates and what can you turn on and off and manipulate and change to actually work out if the network is doing what it should be doing if in doubt just test everything write down the results and see if you can make any links between what you found okay number two then so this is a real big one full obd scan this can rule out any network problems really quite quickly if you can communicate with a module the cam network's probably okay unless you're looking at an intermittent fault then you're going to have to take different kind of testing methods to actually prove that there's a can bus fault before you start going to repair a canvas fault again it's important to go back to the topology to see how the network operates if we check out how the network operates on this one especially with the obd connector we've got an obd connector here straight into the gateway and on some vehicles all of the can networks actually end up at the obd plug and you can actually measure them all right there is really quite useful you can see these breakout boxes that are available you just plug it in and you can you know test each network however that's not possible on this car we've only got one can network down at the obd plug and that is dcan so diagnostic cam so if we can plug into the obd and speak to every module on that network then we know it's okay let's go and see what we've got so we're connected up here i've got my ansel fx-9000 this is pretty cheap scan tool this is and i'm actually pretty impressed with how it performs you can see there we've got a uh automatic vin scan there quite quickly so that's also good news um it's just communicating now then and it's going to be checking for what modules we've got okay so there we're just going through the scan now it's actually pretty quick this tool is you can see there it's got quite a few faults on there and actually quite a few things that aren't have got no faults in key thing is look we've communicated with quite a few modules there so let's have a look at what faults we've got in here then so car access system we've got uh implausible selector lever fault road speed so that's possibly something we're looking at there we know we've got a road speed issue input brake lights as well so that's also abs related so engine control module then we've got quite a few no message problems in there so it looks like the transmitter is dsc it's missing a message from the dsc we've also got road speed another no message there from steering column road speed signal transmission is also message from dsc steering angle so a lot of messages in there here we are so for the airbag light we've got no message for vehicle speed footwell module so that's our body control module in this car we've got brake lights no message driving speed that might be why the wipers are going full blast so one thing we might want to do then is actually go and check the abs so let's just look for the abs control module in this list okay it's not looking good right doesn't look like we've got abs control module here so that's something that you've got to be really careful with some of these scan tools is they won't actually recognize that a car's got a control unit that should be there but it hasn't responded so what we would really like the scan tool to do is say hey abs should be there but it's not responding this is something you should look at whereas what we've got here is just a list of everything that has responded and the fault codes associated but what we should be able to take from this is that you know the canvas network itself is is probably okay on this car so we can see there then the abs isn't communicating on this car if you've ever got any modules not communicating the very first check you should do is the power supplies and the grounds so check the fuses check the grounds and make sure everything's all right there before you start ripping the canvas network apart okay so if you've confirmed that you have got a network problem then you're gonna need to start diagnosing it so step number three is just doing some quick checks with the multimeter we don't need to go out with the scope straight away there are a few tests that you can actually do with this now one of the most popular ones that people like to do is the resistance check across the kanhi and can low so what you're looking for there is a total resistance of 60 ohms now this isn't the be-all and end-all it doesn't test the whole network really all your testing is two ends and i've got a really popular video on this go and check that out and it goes into depth actual resistance checking of the canbus network the other thing about the resistance chair because it only works on a high-speed network so on this car here two of the networks are high-speed networks that's the chassis can and the powertrain can however the body can is not high-speed network that is a low-speed network okay the green one here is actually most bus it's not canon at all it's quite different so if you've got a low speed network then that resistance check looking for the 60 ohms doesn't work it's not a valid test for that however some of the basic tests we can do checking whether there's any continuity between ground or power supply or even still checking whether there's any continuity between the two wires that's that's a valid check and it's a good place to start so what you can also do is actually check the voltage on the wires so it's a really quick check to just see if you've got a voltage that's in the right kind of area so for a high speed canvas network we'd be looking around 2.6 volts on can high and about 2.4 volts on can low however this does really depend on the amount of modules and network activity you've got on the car so the more modules and the more activity you've got the voltage that you read might be slightly higher and it'll be actually slightly lower on canlow because low speed can works on different voltages when you're using the voltmeter to measure those networks the reading is going to be slightly different so you'll be looking for something like 4.3 4.4 on can high and around about 0.5 0.6 on canlow if the voltages you read in there are both exactly the same then you could have a short together should have been confirmed by your resistance check um if you've got both voltages down at zero volts that might indicate a shorter ground which would also have been picked up on your resistance check if you've got some voltages that don't look quite right then what you could be looking at there is an open circuit or maybe a resistive short circuit right if you're anything like me usually miss out step three and go straight to the oscilloscope because it can tell you so much more about what's happening on the network step four is get the oscilloscope out so i like to use this picoscope 2204a it's really cheap and it does a great job at picking up the canvas network on on any vehicle and it can be picked up for as little as 100 so this will tell you exactly what's happening on the canvas network we'll be able to see short to ground short to positive short together we'll be able to tell if it's open circuit and we'll also be able to use it to help identify intermittent faults it'll also help us pick up resistive faults so resistive short circuits or just resistors in resistance in connectors so let's take a look at what we've got on this car i will save these waveforms and you can access them to have a play with yourself so hit the link in the description and i'll send you the link to the waveform library where you can access all the waveforms that i create on the videos in my channel okay so i'm connected in on the gateway on this car then and you can see here on the screen that we've got our canvas message okay so this is this message is on uh the low speed can network so quite different from what we're going to see on the high speed network we can see that can high in the blue starts low and then the voltage goes up that's what makes it can high and then on the red there we've got can low so the voltage starts high and goes down so this is what a good message looks like on a low speed cam and now let's connect up and see what high speed cam looks like okay now we can see that we've got a high speed cam network message on the screen there so as we can see it's quite different rather than the voltage going and crossing over each other from kanhai and canalo they actually start in the middle and go out away from each other so it's also a bit more squashed up because this is faster so what we'd have to do is reduce the time setting a bit to see that message a bit clearer so there we are so there we go and that's our good high speed cam message i've got two videos on checking high speed networks and low speed networks again go and check them out for more detailed information of how to actually analyze these waveforms okay so now we're on to step five so you've actually connected up the oscilloscope and you've confirmed that you have indeed got a canvas fault whether it's a short circuit open circuit what we're actually going to need to do now is actually diagnose and find the problem which brings us on to step five which is the diagnosis process for canbus and really it's quite simple with canbus it's it's merely a process of elimination so firstly you should go back to your evidence so you know have there been any previous jobs done on the car has been any accident damage you know what other works been done um you know to actually help you localize where to start diagnosing otherwise you might have to just test from one end of the car to the other of course accessing the most easiest things first so first what you're going to want to do is disconnect the modules until you get communication again on the canvas network so this is probably the easiest thing to do i know some modules might be difficult to get to but if you do this and there's still a problem that's when it starts to get a bit more difficult so the second thing you're going to have to do then is actually start finding the connectors in the wiring loom so maybe finding the halfway point in the network go into the connector and actually disconnecting it and seeing if the fault is in the wiring on one side of the car or the other if you haven't got any connectors then unfortunately i think you're going to have to start cutting wires and possibly repairing them after there's quite a lot of no joints and splices that there some manufacturers like to use on um vehicles and they can be quite difficult to find sometimes so again try and find out what the common problems are for the vehicle that you're working on so what was the problem on this car that was causing all that havoc with the wipers and the speed and the warning lights it was actually just a fuse for the abs all i did is remove the 5 amp fuse for the abs and that caused all of those problems there so i think the number one message for canbus diagnostics is always check your basics first

Channel: Mechanic Mindset

Views: 25,083

Keywords: mechanic mindset, picoscope, automotive, diagnostics, picoscope 2204a, picoscope automotive, oscilloscope, automotive oscilloscope, picoscope basics, picoscope training, picoscope tutorial, automotive diagnostics, automotive diagnostics training, can bus explained, can bus diagnostics, can bus diagnostics automotive, can bus diagnosis, how to diagnose can bus, how to diagnose can bus system, how to diagnose can bus fault, hantek, hantek oscilloscope, hantek automotive oscilloscope

Id: k8bJegVxo_c

Length: 16min 55sec (1015 seconds)

Published: Sun Aug 15 2021