CAN-BUS Explained | Everything You Need to Know About CAN-BUS | CAN-Bus Diagnostics & How It Works

hi everyone welcome to Automotive diagnosis  YouTube channel uh today I'm making this video to explain everything needed to understand and  to inspect and repair the CAN-BUS in the cars because I've seen many questions about the  CAN-BUS first of all for understanding uh the CAN-BUS basic itself and how to inspect the  CAN-BUS so in this video I'm gonna start from the canvas basic so I will explain how many types  of CAN-BUS we may have in the cars and how these CAN-BUS are connected to the cont

rol units or to  each other and how you can find it uh in the car as well after understanding the CAN-BUS itself and  the structure of the CAN-BUS we will see how we can check the CAN-BUS resistance then the inspect  the CAN-BUS voltage and we're gonna do this to only with using a multimeter so it's going to be a  quick inspection then we will see uh what's gonna happen if we have any problem in the CAN-BUS  like a short to ground and how we can find it just using a multimeter how we can find if

there  is any short to ground in in any of the the cables then we will have a look at the very form of the  CAN-BUS we're going to use the picoscope to read the waveform of the CAN-BUS and we will see if  that's short to ground happens on the CAN-BUS what's going to happen to the waveform when you  are reading the waveform using the picoscope okay so first of all before starting to talk about the  basic of the CAN-BUS it's really important to know why do we need to have a CAN-BUS first of all i

f  you compare these two cars one from 2002 and the other one on the right is 2023. they are both  same cars they are Toyota Camry but comparing these two what's gonna tell you uh obviously  comparing these two the first thing which is gonna come to our mind is how many new technologies  uh we are using right now on the New models so obviously the new model  doesn't have only the external features it's going to have so many electronic  control units so many new systems and new technologies and o

bviously so many wiring and so  many connectors if you just use the conventional way to connect all these control units together  what's going to happen to all those wirings this is the standard configuration if we just  use the normal hard wire for sending any signals between the units all right so what's going to  happen we will have too much wiring we will have so many connectors and believe it or not many  problems on the electronic systems uh come from actually from the connectors and from

the wiring  and when it comes to repair any electronic system having so many wiring and so many connectors uh is  going to make our life so much harder so instead of using a standard configuration uh we need to  find another way to minimize this wiring as much as we can so the best solution was using a CAN-BUS  which is a network to minimize the wiring as much as we can as you see in the CAN-BUS configuration  we have way less connectors uh when we compare it to the standard configuration uh whe

n I compare  these two I'm not trying to say that we don't have any hardware connection anymore we just have the  CAN-BUS no of course not but can bus is there to minimize the need for having all these uh wiring  so it means if if we need to send one signal to multiple units we don't need to use many hard  wires to send this signal individually to any control unit we can just use the network to share  it with other control units for example here so if you look at this configuration you will unde

rstand  what I'm trying to say so what you see on the left right here this is the crankshaft position sensor  which is going to send the engine RPM signal to engine control module so obviously we have  some other control units which need the engine RPM signal but do we have multiple crankshaft  position sensors no we don't we only have one so it means we only have one crankshaft position  sensor to read the engine RPM and send the signal to engine control module which we call it ECM here  so wha

t's going to happen for other control units that need the engine RPM signal I'm gonna just  mention some of them because there are so many units so many control units that need the engine  RPM for example right here we have EPS electronic power steering which needs the engine RPM  signal to to know when engine is started we know the four wheel drive system we have the  aircon air conditioning also need to receive the engine RPM signal we have ABS or ESP uh and  we have transmission control modul

e as well and what we have on the right is  the instrument cluster obviously this unit needs the engine RPM as well to  uh to show the engine RPM to the customer so in this case instead of uh sending the signal  individually to all control units what's going to happen ECM is going to share the information  using the network so what you see right here this is actually representing the network and  ECM is gonna send the engine RPM using this network to all these control units so we don't  have ind

ividual wires for each single signal and this is only one example because there are many  signals that ECM needs to share with other control units and obviously other control units need to  share some information with uh with some other units as well so what's going to happen instead  of having so many hard wires we just have one network right here to share the information  so it means any of these control units like uh electronic power string this one can send the  information uh through the CA

N-BUS it can share the information through the CAN-BUS for all other  control units or it can receive the information uh from the CAN-BUS so you see how uh how  much this configuration is going to minimize uh the need for wiring and for connectors uh so let's talk more about the CAN-BUS  itself let's see how these control units are connected to the CAN-BUS so generally as you  see here all the control units are connected in parallel to the CAN-BUS so it means canvas is  a a multi-master network

it means if something happens for one of these control units canvas  still is gonna work so we can say CAN-BUS is a multi master Network it means every control unit in a CAN-BUS can  send and receive information individually so do we have any other physical control unit  externally that we can find and we can see and we can say this is actually the can  controller no because the CAN controller is built inside any control unit which is  connected to the CAN-BUS so what we see here 10 physical int

erface so this is the can  physical interface so it means that can I see is actually installed inside any of these control  units so it means if this control unit receives any signal from the CAN. this can physical  interface it's going to receive the information uh is gonna convert it to a message that internal  program of this ECM can read and then it's gonna send it to the internal program okay so all  control units are like this one so you don't see any physical control unit that you can poi

nt at  and you you say this is the uh you can can control there no the only thing you see is just the normal  control units inside the car and this uh Twisted wires a pair of Twisted wires which actually  represent the CAN. so uh our can boss is actually made of uh just a pair of Twisted wires as you see  right here between these two uh wires one of them is called can high the other one is called can  low so between these two I can say this one is can high and the other one here is uh CAN-LOW so

what do I mean by saying can high and can  low, uh am I referring to higher speed and low speed? no, not at all yes obviously we have a  high speed can we have low-speed can we have different classes of the CAN that each one of  those classes uh is going to give you different speed but here when I say can high and can low  I'm not referring to the high speed or low speed, what's between these two Twisted wires they have  different voltages so when I say can high and can low I'm actually represe

nting to each of these  two wires because one of them is going to give you higher voltage the other one is going to give  you lower voltage so when CAN-BUS is functioning the voltage on can high is going to change from  2.5 volts to 3.5 volts so this is the voltage on can high but what about on the can low, on the  can-low voltage is gonna drop from 2.5 to 1.5 so this is actually the amount of voltage that  we can receive and we can measure on the CAN-BUS we will see how we can uh inspect and ho

w we can  measure the voltage using a multimeter and using a picoscope so it's really important  to note that what we are talking right now about the CAN-BUS it's  actually the highest speed can which is normally sometimes is called C-CAN okay so this high speed can has all these  features because because this voltage that I told you it's only for the C-CAN when  we are talking about the different type of can like body can this voltage is going  to be different so this voltage is only for on the

or C-CAN okay so what is the specific about this C-CAN  is actually the speed so normally uh this class of the can is going to give you this speed  between 125 kilobit per second to one megabits per second this is actually the other Advantage  when we are using the network not only we are using less wiring less connectors and uh  troubleshooting procedure is going to be much easier but also we are transferring the  information much much faster which is gonna make all these systems more reliable

all right we  already know that we are talking about the C-CAN and as you see all the control units in the secant  are connected to can high and can-low in parallel but we need to we need to think about uh these two  point of the circuit as well obviously we cannot connect these two circuits together to make a  full parallel circuit because these two wires each one of them has different voltage because one  of them is the can high the other one is can-low and on the other hand if we don't conne

ct  these two together what's going to happen we won't have a parallel we won't have a full  parallel circuit we need a parallel circuit to stabilize the voltage otherwise a serious problem  is going to happen to our issues so what's going to happen how can we connect uh these two  lines together without having any problem so what we have here we have terminating  resistor 120 ohms on each end so what's going to happen by having these ones  we won't have any other problem for connecting these tw

o lines together it's really important to  remember that these two terminating resistors only used on C-CAN so if you're troubleshooting the  body can you won't have the terminating resistor anymore so uh where are the locations of these  stimulating resistors normally most of the time uh this one most of the time is inside the ECM  so I haven't seen anything different on most of the cars I've seen of one term it's resistor  is installed inside the ECM but what about the other one the other one

can be different I've  seen many different cases for the other one sometimes it's uh inside the ABS or uh ESP module  sometimes it's inside the instrument cluster I've seen I've seen that sometimes inside  the uh interior fuse box IP junction box and sometimes it's an external uh resistor so  for for for finding this one you need to have a look at the wiring diagram to see uh where is the  location of the terminating register but I'm gonna explain how you can measure the total resistance  for uh

uh for the CAN-BUS so as far as we know we have to uh terminating resistors each one 120  ohms and we and we know that this circuit is full parallel circuit so later on I'm gonna explain how  to inspect and how to measure canvas resistance but it's really important to know what's going  to be the total resistance when you are measuring so this one is actually a parallel  circuit so for checking the total resistance in a parallel circuit we  need to just use this Formula 1 by or total is going t

o be equal to 1  divided by R1plus 1 divided by R2 Okay so here we have R1 and R2 these two are  referring to the Terminator resistor so we can say 1 by 120 plus 1 by 120 right so it's going to be  like this 1 by R total is going to be 2 divided by 120 which is going to be 1 by 60. okay so the  total calculation is going to be our total is going to be something close to 60 ohms. so this is  what we are after okay so when we are checking the CAN-BUS resistance uh we are actually going to  measure

something close to 60 ohms and I'm gonna uh show you guys how to find the  inspection point and how to measure so I already told you that we have the C-CAN  or powertrain can so some control units like the engine control module uh transmission control  module four wheel drive electronic power string aircon ABS ESP uh and instrument clusters  all these units are connected to the c-can we may have some other control units because  uh right here I'm not referring to all the control units because e

ach different  car may have more or less control units but on the other hand we have some other uh some  other classes of the CAN as well like the body cam so body can normally is used for communication  between some control units inside the car and I normally it's going to give you less speed  between these control units you may see some of them which are connected to uh two different  type of CAN For example instrument cluster so this cluster is connected to C-CAN  and body can at the same tim

e or this one smart key control module in this case is  connected to a powertrain CAN and body can but between these ones sometimes we have some  information that must be sent from one unit in the C-CAN to another unit in the body cap  for example the reference for vehicle speed signal is ABS and ESP control unit but some  other control units like the BCM body control module might need this information as well for  example to lock or unlock the doors automatically so what's going to happen BCM i

s connected to the  body can but ESP is actually on the C-CAN so these two don't have any direct connection so how how  can these two controlling share the information that's exactly the time that we have the Gateway  okay so Gateway is actually one control unit which is connected to two different type of can to  share the information between them so it means when Vehicles signal is needed on BCM ESP is  going to send the information of the vehicular speed through the secant to instrument cluste

r  so cluster is going to receive the information in a C-CAN then it's going to confirm it to another  format for B-CAN and it's going to send it in the weekend so cluster is going to work as a gateway  to receive the information from one unit in a C-CAN and convert the signal to a B-CAN to send  the information to that control unit so as you see as I said earlier smart key control module  is connected to uh C-CAN and B-CAN as well at the same time but this one is not this control  unit is not p

laying a Gateway role Gateway in this case is on the instrument cluster even if a  smarty control module is connected connected to uh two can at the same time that one is not going  to play a Gateway group the other important item is actually this one which is your scan tool  your scan tool is going to get connected to the c channel as well from DLC connector so you  have the DLC or oBd2 connector which is connected directly to the c-can to diagnose the to diagnose  all the contributing is conne

cted to the C-CAN so this is really important but your scan tool  to diagnose other control units which are not connected to this C-CAN it's going to use another  diagnosis communication line which is normally uh sometimes which is sometimes a K-line so that's  different for example in this case your scan tool is not going to diagnose the PCM using  a C-CAN so this this is really important fact uh to know okay let's have a look at this wine  diagram for one car that has uh three different type o

f can so we will see what control units  are connected to each one and we will see the Gateway for each one as well for example  this one is actually C can at the top left so some control units like uh electronic  power steering we have the SRS or airbag we have the steering angle sensor right here  we have the smart parking assist tire pressure monitoring system electric parking brake module  or EPB Lane keeping asset system right here uh we have engine control module right there  in this case

a vacuum pump is connected to the CAN-BUS as well and blind spot detection system  as well so these are the units which are connected only to the C-CAN and couple of other units right  down here like the TCM transmission control module ABS is right here as well or ESP if your car has  ESP obviously ESP is connected to there C-CAN so we have some other control units uh  in between like the navigation system AC panel instrument cluster and a smart key  control module so these units these all these

units are connected to the C-CAN but with between  these ones we have we have gateways as well if you look down to the right or to the left  we have B can in here for body cap and M-can draw it on the left for multimedia can so we have  two other cans here multimedia- can and body-can so for multimedia can we have the audio system  and amplifier these two are connected to uh the multimedia can, and as you see uh we have  two other control units uh AC control units right here and navigation as w

ell between these two  one of them is actually the Gateway between the M-CAN and C-CAN so we can I can just write it  here uh uh AC is going to be actually Gateway for C-CAN and multi-media CAN so in this case we already found  one Gateway navigation is not a Gateway in this case but what about for the B-CAN for the body can  for the body can we see the BCM we see the head unit we see driver IMS module or integrated memory  system we have the smart junction box as well but right here we have a s

mart key control module  as you remember we had it in the previous uh uh section and we have the instrument cluster  as well and I explained already that between these two only instrument cluster is the Gateway  between C-CAN and body CAN so it's going to be cluster will be again Gateway for C-CAN and body but how can we reach to the can bus  to to start inspecting the CAN-BUS as I said earlier this video is talking only  about the C-CAN even if we refer to multimedia can and body can earlier it

was just to show the  structure to show the gateways but this one is this but this video is generally talking about the  Diagnostics procedure and and uh the basic of the C-CAN or high speed cam so uh obviously we need  uh some point to reach to the canvas to measure without having any problem without actually trying  to reach to any other section of the wiring when we are trying to do the quick inspection as I  said earlier your scan tool is going to be one part of the CAN-BUS when you try to

diagnose uh  the car because when you connect your scan tool to DLC connector your scan tool is going to be  actually one part of the CAN-BUS so it's going to send the request for the information and all  other contributions will be communicating with your scan tool to send the information so for  finding the secant high and C can do you can just have a look at here this is the C-CAN high  and this one is the C-CAN low but uh on this car manufacturer these numbers are just like this  one two thr

ee three and eleven four uh for the can high and can-low but please uh just try to  have a look at this one as well because these numbers are only for electronic troubleshooting  manual but those numbers that we need are actually the numbers on OBD2 itself okay so our  number is going to be number six for can high so you CAN-LOW number 14 on C-CAN so the only thing you need is uh to find the  OBD2 connector which is most of the time on the driver's side find these two pin numbers 6 and 14  and w

e know that the pin number six is going to be for the Can-high and pin number 14 is going to be  for the can low and the rest is going to be what uh I will explain to you guys on the car uh to uh  to inspect the CAN-BUS resistance to inspect the CAN-BUS voltage and to read the waveform so the  first step for checking the canvas is to check the total resistance so as I said earlier we can you  can reach to the CAN-BUS from the OBD2 connector just as I did find pin number 6 and 14 and check  the t

otal resistance when ignition switch is off so the total value should be something around 60  ohms so we already we have 62 which is acceptable but you need to make sure ignition switch is  off but what happens if one of the CAN-BUS resistance is it's not working so what I do I  remove the ECU engine ECM connector just to uh to disconnect the CAN-BUS resistance inside  the ECM and I'm going to check the resistance again and what I read here as as you see is  going to be something around one to a

ny ohms so this value shows one of your CAN-BUS  uh terminating resistor is not working next step is going to be to check the voltage on  the CAN-BUS so what I do uh I'm gonna select the voltage on my multimeter and I go one by one uh  this time ignition switch must be on uh I go one by one I check the voltage on CAN-BUS high as you  see I have 2.6 volts and just make sure the the black cable is connected to good ground and on  CAN-BUS low I'm gonna have something around 2.4 2.3 uh volts I can a

lso check the short ground  for CAN-BUS and so uh continuity function is going to help me for this. ignition switch must  be off I can put my red cable on can bus high and CAN-BUS low individually one by one and the other  cable must be on the ground I shouldn't have any continuity during this test next step is going  to be reading the waveform using the Picoscope, so what I'm gonna do I'm gonna put the a red  prop on the CAN-BUS and the black one should be connected to the ground and just to ma

ke  sure that CAN-BUS is working I'm gonna start the car to make sure all the units connected  to the CAN-BUS uh are sending and receiving the information so I'm gonna have a good way  for it so this is the waveform for the CAN-BUS eye so as you see the waveform uh is changing  from 2.5 to 3.5 volts and if I change uh the red prop to the CAN-BUS low I'm gonna have  the voltage dropping from 2.5 to 1.5 voltage so here you see the value on the  CAN-BUS high I'm gonna have the voltage changing betw

een 2.5 to  3.5 volts this is what I get from on the CAN-BUS low my voltage is going to drop  from 2.5 to 1.4 but what happens if I do have any short to go around on one of those CAN-BUS  wires like the CAN-BUS high or CAN-BUS low so of course I I won't have any communication but  what's going to happen to the waveform so this is the CAN-BUS 5 with waveform when everything is  normal but as soon as I make the shorter ground you see the voltage is gonna disappear and  what I'm gonna have is just

a really really bad waveform around zero volts so  this one shows that the CAN-BUS is down and it's not working anymore thank  you very much for watching uh if you liked the video please don't forget to like and  share the video with your friend thanks a lot