Can-bus Trouble

[Music] [Applause] [Music] hi everybody and welcome to a new episode of diagnose Dan today we're working on this BMW 5-series and the customer complaint is it has got no speedometer and it has got a transmission failsafe program and what I'm trying to do right now is to confirm the customer complaint now we'll show you in a second now that we confirm our customer complaint we can continue our diagnosis confirming your customer complaint is a very important step in any diagnostic process because if you didn't confirm the complaint it's very hard to confirm the fix now let's start out by reading some fault codes let's go to drive and since we had a transmission failsafe program let's read the codes in the transmission first and we've got a know calm let's try again and still know calm let's try let's try the PCM the engine electronics and we have got a know calm as well so let's back out let's go to chassis and let's try the ABS and see if we can communicate with that now it's taking quite long so I guess it's gonna be in no calm as well let's see yep and no calm so let's back out and let's go to body and since we had no speedometer let's go to the instrument cluster and we can't communicate with the instrument cluster so let's read fault codes and we've got some ten fault codes now what these codes are basically telling us is that the instrument cluster is getting no information from the transmission module or from the ABS module now we confirm this because when we tried to read the codes inside the ABS module or the transmission module we couldn't communicate with it either now why would the instrument cluster need any information from the transmission or from the ABS module now on the instrument cluster is the little indicator which indicates in what gear you're at now that information is provided by the transmission module and remember the speedometer that wasn't working Road speed information is provided to the network by the ABS module from this point on you could take many directions the direction I like to take is take one of the modules we can't communicate with and do the basic checks just check power and grounds and the communication lines and that way I hope to eliminate the problem and find out what is wrong now what module you should take depends on the car you're working on just take the one that is easiest accessible on this particular car is the ABS module now we decided to check the basics of one of the modules we can't communicate with again on this car we've chosen for the ABS just because it's easy accessible on this particular model now this is the ABS unit and this is the wiring diagram it has got three main feeds on pin two six and twenty three coming from the fuses over here it has got two main grounds on pin 1 and 5 and it's communicating by Ken high and Ken low on pin 40 and 24 now in order to do some measurements on this ABS unit we need to back probe the pins now to reach them we've got to take this little plastic cover off so let's disconnect the connector there are little clips holding it down and when it's out of the way we can easily back probe the wires now this red wire on pin 2 is one of the wires we need to check is one of the three main feeds of this ABS module now in order to do the measurement we need to back probe it now when you back probing a wire make sure you don't damage the weather seal surrounding the wire now in order to do this place your needle as close to the wire as you can and gently follow it down all the way into the pin this way you make sure you don't pierce for damage the weather seal now let's start with the power and the grounds a back probe the two ground wires with these black back probes and a Beck probe the three main feeds with these colored ones now let's connect my test light to one of the negative wires and let's check the powers one two and three and let's try again using the other ground one two and three so the powers and the grounds on this unit are fine and it's not the reason why I can't communicate with it now the power and grounds on this unit are fine so those are not the reason we can't communicate with it now the next thing we're going to do is check the communication wires now in order to do this we've got to know what to expect so before we going to start the measurement let me take you through the base of canvas now let's ask ourselves the question why canvas and let me give you an example this ABS module is connected to the wheel speed sensors it uses the wheel speed sensors to calculate the road speed now there might be other modules also interested about knowing the road speed for example the transmission it needs Road speed to calculate when to change gears now another module that might be interested in knowing the road speed is the instrument cluster it needs the road speed to determine what to indicate on a speedometer now without can all these modules would need their own wheel speed sensor or they needed to be wired to the same sensor now using can the information is put on a network by the ABS unit for all modules who would like to know dramatically decreasing the amount of wiring and simplifying the system now not all the communication between modules in a car is canvassed you've got a little bus flex rail mouth bus and you've got many more and even when you're talking about canvas there are differences you've got low-speed canvas which is a one wire system and we're not going to talk about it in this episode you've got mid speed canvas which is mostly used inside of the car for the comfort systems and you've got the high speed canvas which is usually the powertrain canvas which includes the engine the transmission and the ABS now when you're working on canvas you've gotta know what canvas you're working on so let's take a closer look to the differences between mid speed and high speed canvas now let's select a mid speed canvas and let's take a look at a known good and as you can see the voltage on a mid speed canvas goes from zero to four four point three volts and the other line does the opposite now let's take a look at the voltage on a high speed can line so let's select high speed can line and let's take a look at a known good let's bring it down a little bit now a high speed can bus goes from two now volts to three net volts and the other line is going from two net volts to one-and-a-half volt so forth it's wise both can buses are totally different so looking at the voltage it's telling you what canvas you're working on I've made a simplified drawing of a canvas system a canvas system uses a twisted pair of wires but why are the wires twisted of course they are easier to recognize but that is not the main reason why they have done it they've twisted two wires so they're always close together and when something would happen to the voltage in this wire it's likely it will also happen in this wire like when an outside source is creating an induction voltage in this line it will also create an induction voltage in this line so the signal voltage raises in this line it will also raise in this line but the difference in voltage between can high and low will still be the same and the system will still be operational so it makes it more robust now I've also drawn to 120 ohm resistors at each end of the twisted pair of wires now in real life these resistors are built within two of the modules connected to the network now it doesn't matter if you have two modules connected to the network or in this case three or even ten there always two with a 120 ohm resistor built into it now let me explain why this 120 ohm resistors are built into the network now to do that you've gotta imagine they are not there let's imagine both these resistors aren't there we just have this twisted pair of wires now imagine a message being sent on this wire with that the resistors the message would travel to the end of the wire but at the end of the wire there would still be energy left because there's almost no resistance within this copper wire now the message would come back because there's still energy left and it would go back and forth a couple of time until all the energy is lost this is what we call an echo now we don't want any echoes on our communication lines and this is why the resistors are built within the network now if a message has been sent the rest of the energy that is left is consumed but is to 120 ohm resistors now that we know a little bit more about the basics of our 10 Network we can start doing some measurements on it now let's start by checking the resistance between both communication wires let's do it by using a simple ohms jet now I have back Pro they can high and the can low wire and we're gonna perform a resistance check using the multimeter so let's put it on resistance in ohms and let's check the resistance between can high and Kenna low and it's reading 59.7 ohms so almost 60 ohms now I told you guys there are two 120 ohms resistors built within this network so have we got a problem or is this a normal reading now we just did a basic resistance check between can high and can low and we measure the resistance of 60 ohms now is this a normal reading where is something wrong is this may be causing the no calm but actually the reading is just fine when you've got two 120 ohm resistors placed parallel to each other the total resistance is 60 ohms now if you're having a hard time understanding this let me try to explain by a simple drawing now let's imagine we've got a river and on one side of the river people are waiting and pushing to get across to the other side now let's call the pushing of the people the voltage and let's scroll the amount of people crossing the bridge in a certain amount of time the current that the bridge itself we're gonna call a resistor in this case I called the bridge 120 ohms now although the bridge is helping the people to get across to the other side of the river it's also a resistance it's the only place to cross the river and only one person at a time can cross it now would it help the people if we place a similar bridge parallel or next to the bridge that's already there now let's try it let's draw the same bridge or at least that it's supposed to be well it's also called 120 ohms now although we have placed another resistor twice as many people can now cross the river so instead of one person now two persons at a time can cross the river so is the resistance now higher or lower well our resistance has been cut in half we've got twice the capacity so instead of 120 ohms or twice 120 ohms the total resistance because twice as many people can cross the bridge is only 60 ohms now that we've got that covered and we know that our resistance of 60 ohms is just fine let's bring out the oscilloscope and take a look at the waveforms on our signal wires now these yellow and black and yellow and brown twisted pair of wires are high speed power train communication wires now I've back probe those there are the same wires we did the resistance check on and I hooked up the oscilloscope so let's see what the way from look like now the ABS module is connected to the power train canvas now the power train canvas is a high speed canvas so we're looking for the tune f 2 3 manifold signal on one wire and the tuna to one 1/2 volt signal and the other wire now let's select high speed canvas and let's start the measurement and I already pre-loaded and known good so this is what the signal is supposed to look like now when I press play it will display the waveform that's on our signal wires right now now you decide whether this is our problem why we can't communicate or whether everything is just fine now that waveform looked nothing like our known good the voltages were way higher so there's definitely a problem on our powertrain canvas the next step is to figure out what's wrong now to do that we've got to take a look at a wiring diagram of our powertrain 10 bus this is the wiring diagram of our powertrain canvas it has a yellow and black wire and the yellow and brown wire connected to our prowl train canvas is the engine or PCM the transmission control unit the ABS module the instrument cluster and the steering angle sensor but only if the car is equipped with DSC now the next test I would like to perform is called the unplug it test if one of the modules on the network is responsible for disturbing the signals on the Kin wires unplugging this module from the network should make the signals return to normal now since we're already back probe at the ABS module and this one is the easiest accessible let's start over there now let's start the measurement and let's start the unplug it test and the first module I'm gonna unplug is gonna be the ABS module so let's unplug it and it seems we got lucky the first module we're disconnecting the ABS module is causing the problem now let's plug it back in and let's unplug it again our ABS module is definitely causing our problems we got very very lucky the first module we disconnected what's causing our problems now we don't get lucky every day at least I don't but it always seems to be the last one you're disconnecting or the one which is hardest to reach now if you pay really close attention you notice that even with the ABS module disconnected our signal voltage was slightly higher than unknown good so let's take another look at our recorded waveform now as we take a closer look to the recorded waveform of our high speed canvas with the ABS module disconnected we can see that the voltage on Ken High and ken low is slightly higher than our known good now have we got another problem or can we explain this that it's actually quite an easy answer to the question why is the signal voltage a little bit higher with the ABS module disconnected now remember I told you that the resistance between Ken high and Ken alone should be around 60 ohms just like our meter is reading right now I also told you somewhere in this network there are two 120 ohm resistors now let's see what happens when I disconnect the ABS module from the network the resistance goes to one hundred and sixteen point six ohms that's very close to the one hundred and twenty ohms that means that one of the two resistors is within this ABS module and without the ABS module connected the system is running on only one resistor causing the voltage to be a little bit higher now the next thing we need to do is replace that bad ABS module [Music] [Applause] [Music] [Applause] [Music] [Applause] [Music] [Applause] [Music] [Applause] [Music] [Music] well our ABS module has been replaced now let's bring up the scope let's see if our communication has been restored I've got the scope hooked up the moment of truth now just let me know what you guys think about it have we got a fix we're inside the car now let's see if we can communicate with the power train can buzz again and it looks like we were on speaking terms again so that's great and some can faults but that was to be expected not a big surprise let's try another module let's try the transmission yep and communication is restored some 10 faults over there as well no big deal that was to be expected it looks like we have a fix we started this video by confirming the customer complaint now the customer complaint was a transmission failsafe program and no speedometer we ended up with a canvas fault now because the network was down the information about the road speed was no longer available for the instrument cluster and the transmission so the transmission didn't know what to shift and the instrument cluster didn't know what to display on a speedometer so at the end it all makes sense now what I'm doing right now is confirming the face are you curious now if you liked this video and if you want to learn more please subscribe to my channel and when you hit the little bell you will get a notification each time I post a new video and remember diagnosed then fix it again see you next time guys well it seems to be my lucky day so I'm going home now and who knows I might get lucky again [Music]

Channel: DiagnoseDan

Views: 425,368

Rating: 4.9543276 out of 5

Keywords: Diagnosedan, bmw, canbus, can-bus, gmto, scope, oscilloscope, fix, scannerdanner, south main auto, eric the car guy, new level auto, diagnostic, educational, faultcode, autologic, abs, waveform, pine hollow auto diagnostics, thomas exovcds, realfixesrealfast, scantool, snapon, car, dsc, transmission, instrument cluster, scotty Kilmer, bodgit and leggit, speedometer, failsafe, garage, training, course, explained, engineering explained

Id: uKnQI2IScPU

Length: 27min 34sec (1654 seconds)

Published: Sun May 13 2018