CAN BUS - HOW TO FIND OUT IF IT'S GOOD OR BAD

[@SuperMarioDiagnostics]

One thing I totally forgot to mention is to know your scope and the circuit you're working on! I would highly advise that if you are going to reference to CAN low, don't use any other channel grounds. Play it safe, some scopes have isolated grounds, others have common grounds. Referencing your ground to CAN low in a common ground scope while testing another circuit that is referenced to ground will short the CAN low to that ground! Attempt at your own risk.

[@l.franco9050]

Very good point its good to know what type of tests must be performed and what a good reading looks like ...👍

[@JoeBob79569]

This is interesting. I just got my first scope yesterday, and when I measured my CAN, both the high and low signal looked exactly the same. It looked like I had 2 CAN low signals. I thought it might have been a glitch with the software (Hantek 6022) and that one signal was inverted, but it might also be a ground issue like this. I put both grounds to battery negative.

[@DonutCzar]

glad you mentioned this cause I was going to comment on that risk. Nice video!

[@SS-U23]

Very good point! Scope positive to CAN H and scope ground of the same channel to CAN L to get the difference between the two levels. Thank you very much!

[@joelaplnski5394]

Got to love the guy, sweaty, dirty face, under pressure from the shop, showing us how to. thumbs up Mario!

[@SuperMarioDiagnostics]

😂 Thanks Joe!

[@Hartzelhutch]

Thanks for the great tip. After wrenching for 45 years I am still amazed at how much there is to learn. If you don’t learn something new each day, you haven’t had a good day.

[@mechanicmatt871]

That signal looked like there was something to be concerned about, this is definitely one to remember, doing the math. Thanks for sharing this information it's really appreciated.

[@VoltageDropDiagnostics]

I love all of your videos, but this one here is full of so many tips in such a short amount of time! Great job, again!

[@stephencook4611]

Mario, since you are grounding the scope through the chassis ground you could be picking up noise in the ground circuit. When the engine is first started the alternator output rises. After the engine warms up some the alternator output will normally drop. This could be the cause of the waveform pattern you are seeing. I have always felt it is best to ground straight off the battery whenever possible. This should help eliminate or clean up a signal on your scope. just a thought. I really like your videos.

[@SuperMarioDiagnostics]

Actually in this whole video i never turned the engine on. The only thing that had any real current was the fuel pump and throttle body(which is wired directly to pcm)

[@stephencook4611]

@@SuperMarioDiagnostics Okay, good to know. This is odd. I would have chased to pattern issue too. just one of those things we have to deal with. Thanks for the tip. Keep up the good work.

[@SuperMarioDiagnostics]

Yeah i chased the pattern. Every time the throttle body would reverse its polarity, it threw off the bus waveform. There's a tsb on several gm vehicles saying that the tb will make the bus body and is considered normal. I had completely forgotten about it. Thanks for jumping in.

[@howlinhog]

Thanks for the honesty and wearing your heart on your sleeve as they say. I've been struggling with the application of the math channel and your trick of using the negative lead on CAN lo and the positive lead on CAN high was a fabulous find for me. Thanks. Can't wait to get back to work and put it to use. I wish I could attach an image on here I've got a couple files saved from a CAN circuit that looks like I dragged the leads across an electric fly swatter and there was no codes or even a complaint. I was just collecting known goods files and was very perplexed by what I saw. You could say it is the reason I came across this video trying to find as much info on CAN diagnosis as I could shove in my brain.

[@ozzstars_cars]

Nothing like a good rabbit hole ass kicking to gain experience. Good info Mario!

[@CarsExposed]

Tell me about learning the hard way Mario 😊😁... thank you for taking the time to post this 👍👍👍

[@johnfountain8143]

Excellent example of why CAN is used , interference of of the communication line makes the overall differential voltage the same great video thank you ..

[@davesterl]

Nice one Mario, never scoped between the high and low before, must remember that one, cheers dave

[@codysautodiagnosticsprogra8706]

There’s lots of good information in this video Mario especially helping out other guys to stay clear of that rabbit hole that you entered. Does Matt channels are pretty awesome and I never tried using one channel on the CAN high and low like that, so that being said I learned something!

[@BrianMann216]

Excellent Mario! Well done, I use the math channel on the Pico, however did not think of / or know of going between high and low with one channel. Thanks for sharing this.

[@wyattoneable]

Wow, there are of lot of variables to watch for. Thanks Mario.

[@rubengarcia6920]

Thanks Mario I am just starting to experience with the gave forms and you are one of the best simplifying the set ups

[@PineHollowAutoDiagnostics]

Bad ground on the scope at 5:00? Almost got burned today by a similar waveform... :0 Awesome tip with the math channel!

[@kellyspeppers]

Good info, thanks for showing us the signal and the workaround.

[@joemasterman4305]

Great video man! I would have thought there was an issue for sure, great catch! I love employing the Math channel to clean it up, brilliant!

[@spelunkerd]

I scratched my head when I learned that the CAN system uses two wires. This case is a great example of why they did that, to cancel out confusing noise.

[@SuperMarioDiagnostics]

Exactly! Thanks for checking out my channel 👍

[@catzwa]

Wow, I would have sworn that CAN waveform was something faulty; that Math channel is amazing. Awesome stuff!

[@timothycooney986]

I know I'm late to view this video, but, once again, this young man continues to impress. He should be on the faculty of a technical college.

[@train4905]

Dear sir.that was an absolutely brilliant demo.i realy loved the tip ,with using the 1 channel pos and neg scope leads to measure ,the difference beetween the 2 wave forms.superb videos sir.keep up the greatvvids,steve from the uk.

[@weldingjunkie]

Great info Mario that’s really interesting I never thought about using a math channel to double check the signal. Awesome awesome video. Send it lol ... Jay

[@ThePracticalMechanic]

Great information Mario. I ran into similar issue a few times and I chase it for a few minutes before I remember to add a math channel. Since I have a 4423 pico I have to be careful with checking differential signals because mine has a common ground for all channels. I think they changed it on the 4425 and each channel has its own ground.

[@chrishemphill3684]

Just went down this rabbit hole on a paccar with communication issues, I assumed the wavy waveform had to be the issue. The wave smooths out after about a minute of running, it only happens on start up. Thanks for the video I appreciate it

[@DylanRabier]

Wow excellent video. Very good info. Thank you for sharing Mario! 👍

[@iam1smiley1]

Thanks for showing exactly how you hook up the leads, so many channels skip this part and rookies like me get lost.

[@High_Tech_Mountain]

Wow! Great video Mario, looking at that waveform I would’ve definitely thought there was a problem! Great tip on setting up a math channel to see what the computers looking at. As always, thanks for sharing!

[@SuperMarioDiagnostics]

Watch the last part too brother, might come in handy

[@thecaribbean8615]

It's common mode interference. CAN eliminates common mode interference because it is a differential signal. Connecting the scope across CAN high to CAN low. We all learn. Great video. I'm watching because I have a DC offset issue where the DC values of CAN high and CAN low to ground are lower than they should be (out of tolerance). It looks like I'll be unplugging connectors one at a time until I find the module holding the DC low which should result in the DC going back to normal the moment the bad module interface is unplugged. The bad news is that I have a lot of modules! I plan to start with the easiest to access down to the hardest to access last.

[@billyyoder8171]

Thank you Mario. Good job. Have a blessed and safe week.

[@kirkabrahamson1148]

Great info once again Mario. Something else I was told if the can waveform looks a bit off is "Do the lo and hi mirror each other?" that is a good indicator for correct signal, but man I reckon that waveform would have thrown anybody.

[@nickl3872]

Good job, sometimes we learn this way, but you just got to stick with it to the end that's how you learn. Thank you

[@rodvan-zeller6360]

Thanks for making this video. Especially using a regular two channel scope to look at the math.

[@CubasAutomotive]

Wow! Such a good video! So jam packed with excellent info! Thanks Mario!

[@brucebratschi4300]

Thanks for great info. Are you going to show us what it looked like when "hot" and what was causing it?

[@radamstruck]

Thanks for taking the time to point this valuable information out to us!!

[@CortezAutoServiceMobile]

You already saved me time brother truly appreciate it

[@tommymarkham4202]

Good video Mario. Very helpful, I need all the help that I can get with network issues, lol.

[@octaviocarrillo5954]

I actually got lucky and learned this by testing known good cars. It definitely looked weird but the vehicle had no issues. When I got another gm I tested again and saw the same thing. So I figured it’s a gm thing. I did notice the waveform looked different key on vs running.

[@33798]

Hard learned job!👏 That would be great if you upload the whole diagnosis chapter of this hard shifting car

[@paulpaquette1961]

Awesome Video Mario. Thanks for sharing your experience. I like the math channel tip, Soooweeet!

[@raviautoscanning]

Very helpful. Thank you Mario.

[@arthurfricchione8119]

Thanks, Mario for the insight. All your videos are very helpful. Thank you for sharing 👍👍👍

[@1quickchevy2]

Thank you! Great information.

[@vicky-nc3to]

I learned something... thankyou for upload🎉 So i think instead of looking at can high & low waveform, we ahould be looking at the difference betwsen them.

[@FaithTriCities]

When doing math, you can decode, to be sure it is compliant. Sometimes not needed, but if you really want to be sure it is talking, and CRC Check, et al, decoding is a must.

[@locati82]

GRAN VIDEO! PERO CUAL FUE EL PROBLEMA DE ESE VEHICULO??

[@BrianMann216]

Great work as always Mario! Hope you are well .

[@superk4562]

Thanks for sharing Mario!

[@FaithTriCities]

Also, as far as a strategy, make sure you look at topology. If other modules are communicating on the same buss, that means something. I like to tst at the module, not the OBD, if possible, and there are times the OBD will not have the CAN bus you need to test. Todays carys have a gateway, or diag buss, and you cant get to the CAN from OBD. BTW, Mario, what was the Fix???

[@kennethkristensen5537]

Hi super Mario. Thanks for sharing this information. If you have an bad can bus signal. And you measure between can high and low. Yo will only see and straight line?

[@Victor664.1]

seguí al ganso por un dia , ahora se porque y como evitarlo gracias Mario por compartir

[@jamesl197999]

Very helpful information thanks.

[@fire7765]

Thanks for the tip Mario

[@alexandriabowe]

Hope you feel better Mario

[@josecejoco6994]

there is always something that will throw you off and you later on catch it. thanks for the vid

[@stephenmarshall5302]

something else I've learned, thanks mario

[@franknalej6492]

thanks Mario can you show with pico scop you used and with accessory i should bay

[@renatairmarius123]

Thanks man, nice video. Its good when you share your experience. More videos like this. Thanks

[@DmitriyL_Arithmechanics]

Uh oh, after this video I have more questions than answers... I will join Stephen Cook in questioning your ground point -- could be the actual source of the observed "rollercoaster". I would try to rule that out before invoking math channels. The Picoscope team explicitly asks NOT to go "differential" on a CAN bus with Pico4425: "the negative input should not be connected to fast changing signals such as CAN Bus, FlexRAY or some crankshaft sensors that may be effected by capacitive loading." This is from article "Introducing floating inputs" on picoauto website. And with other scopes going "differential" can become a real goose chase if they have ground supplied accidentally through a power supply, sensor on another channel, etc., as that would short the CAN Low signal completely. That would be a bad day!

[@SuperMarioDiagnostics]

You make some true and interesting points. This was a key off to koeo test, so what he mentioned about the alternator isn't taking place here. Wouldn't referencing my ground to a questionable chassis ground mean that the ground is also compromised for many other circuits? You are correct about the risk of going "differential" using a common ground scope along with testing other circuits, I totally forgot to mention that! Yes pico does mention that, but i guess i got lucky as the waveform was unaffected by me referencing to CAN low. But you are absolutely right there. Thanks buddy for the insight! 👍

[@xerxes456]

@@SuperMarioDiagnostics Throttlebody changing polarity could that be a source of the distortion in the waveform?

[@SuperMarioDiagnostics]

That's actually the case. And what led me into the goose chase. Several times, people have mentioned how noisy the throttle body is, and that it'll affect the can bus waveform, there's even a tsb on it. But I totally forgot about it

[@DmitriyL_Arithmechanics]

​@@SuperMarioDiagnostics No alternator involved for sure, but any other high-current load will act just the same. The PCM has several ground pins, and they are all at the same voltage until high current starts flowing through some of them. Depending on which one is routed to your breakout box, you might or might not see the imprint of that high current.

[@SuperMarioDiagnostics]

Dmitriy L. What i do find strange is that only the throttle body has an effect on the can waveform. Nothing else. Even though all pcm circuits flow through one ground wire, through G103(at the block) and direct to battery. The dlc pin 4 is to G200(body). The body is connected through a ground strap to the block near the brake booster, and I had the same concern with the ground. Load tested it and it was fine. All of the components that are provided ground by G200 are fully functional(srs, hvac, sunroof, just about all of the interior) I don't get ignition system noise, injector noise, nothing. The throttle body maxes out at 7 amps. Not to mention if I had a bad ground, my scan tools would've had issues upon key on

[@bethgrabow1825]

I have watched your video. I am not a mechanic. My problem is with low temps. Anything below 27 degrees. I used oscilloscope but the same wave forms. Not sure how you went.

[@alexlongpre4527]

Hey, learning some the easy way is a learning that will be forgotten. 👍🏼 👍🏼

[@stevepark5504]

The pattern of the interference looked familiar. I should have looked closer. I calculated the waveform period off of your waveform. It calculates to about 60Hz,,, power line. That is why it looked familiar. Which means the noise is not on the vehicle( unless it is connected to a 110 powered device, then maybe). The noise is being picked up through the scope itself. As PHD mentioned, a loose scope ground can also cause it. There could be a ground loop if the scope cart is on AC and the vehicle has an AC device connected to it. I used a UPS computer supply on my scope cart to isolate it from mains power and prevent loss of AC from shutting down the scope.

[@SuperMarioDiagnostics]

I have before and after psdata waveforms of this, grounded at the dlc, and grounded direct to battery. No 110 device connected) Another thing is that if this was a power line issue, I'd imagine the noise would be present regardless of the throttle body actuation. It cleans up as soon as the throttle body current flow ends. If you'd like, i could send you the psdata files

[@spot-onautomotivediagnosti7583]

I fell victim to this. Had a 2015 1500, ucodes for bcm in multiple systems. Combination meter gauges would sweep while in gear. Vehicle would lose gear. Fog lights would randomly turn on at times. With no key in the ignition. Scoped the dlc and found that noise with the bcm in the loop, once disconnected waveforms would clean up.

[@Kevin_YouTube]

Thanks Mario for a great tutorial - Once you have the maths channel, have you tried to run the serial decoding on it? It works well and has helped me in the past to ID the problem controller.

[@SuperMarioDiagnostics]

Yes, not often but yep it's a handy tool. Thanks for watching!

[@billshaughnessy3955]

great info . that would have bit me for sure. thank you.

[@410AutoTech]

Awesome tip Mario's we all have been on a wild goose chase and will always sometimes run into it. Was there a power supply circuit open to the t c m?

[@SuperMarioDiagnostics]

No the tcm went incommunicado with heat.

[@tallercabrera1908]

hola mario How can I isolate a module that loses intermittent communication

[@BuggysTowJam]

Very good Mario! Thank you for sharing this video! Thumbs up

[@JoesAutoElectric]

Great video brother and great information! Thanks for sharing!

[@stevepark5504]

The noise is on the ground circuit. Finding out what is wrong with the ground would be a primary concern to me. The grounds at the DLC should be very clean since there are no loads on them to cause voltage drop. If the scope is a grounded input type and the scope is not isolated from vehicle chassis, connecting across the CAN pair would short one side to ground.

[@SuperMarioDiagnostics]

This happens across many gm platforms. If this ground was suspect, so many components would not be working, or malfunctioning, it provides a ground to a ton of components including pin 4 of the dlc.

[@sandyande]

Brillant Mario, what a great tip, thanks for posting ,cheers sandy

[@adrianlowes1848]

Great work dude. Noticed you went to chassis ground, I was always told to use signal ground. Wonder if that would make a difference. However great explanation of using math channel and the other way. Yes we have all chased a few geese though.

[@SuperMarioDiagnostics]

Yeah? I've always been told to use pin 4 😆 either way, the ground integrity has been brought up, so I hooked up the ground direct to battery, same results lol thanks for swinging by!

[@adrianlowes1848]

Makes sense i all ways watch back to tech learning now I a tech for another shop

[@8power0]

GREAT VIDEO MARIO , I CAN'T WAIT TO TRY THIS DIAGNOSTIC TECHNIQUE OUT . THIS IS WHY WE MUST ALL TUNE IN TO YOUR CHANNEL AND I PERSONALLY WOULD PAY TO SPEND A DAY LEARNING THIS KIND OF OUT THE BOX TRAINING . PLEASE SIR KEEP THESE AMAZING DIAGNOSTIC VIDEOS COMING AND WE WILL DEFINITELY KEEP WATCHING . ALL THE BEST AND THANKS AGAIN ! ! !

[@maxl.8804]

Bad / Wrong ground used for scope causes that Wavy signal! I ran into this testing CAM sensors-forgot to ground scope and laptop was plugged into AC power charger--unplugged AC charger-Ran on laptop battery-NO MORE FUNKY Waveform. Ground issue for sure :) Yea like you say-gota know your scope and what you use it on. Pressure from a shop makes us forget and gose comes in chasing us :)

[@SuperMarioDiagnostics]

A bad ground can cause a wavy signal. But that's not the case in this video

[@jharrison6557]

What was the purpose of looking at the TAC current?

[@fredsalter1915]

So there must be some kind of AC component being injected into the CAN bus?

[@tonyle7909]

Hi there, was wondering if its a Picoscope thing how you have your signal to trigger off the Throttle body current? - Fairly new to scoping and never heard of this term, as usually I would just crank the vehicle and get a waveform with manufacture labscope.

[@flatratemaster]

Great tip Mario

[@patelvivek4888]

This is a life saver ,Great Video Man 👌👌

[@gilbertomoran7420]

Good information just like in all your vids . Keep it up man .

[@elevensevenonetwo]

Mario I have that same pattern I use math channel same mess unless I picked wrong math channel I used A-B. I am probing in back of BMW X3 transfer case module when at dlc with box both signal 2.5 no data? But car runs 2 scanners see module no com issues just no message.

[@timezupbabi]

Just answered a very important question I had.

[@padraiggalvin2807]

Great video again Mario. Thanks for sharing this. If this Network was in trouble and if there were a lot of codes being thrown, which part/modules would be likely faulty in a car or could it be wiring??

[@SuperMarioDiagnostics]

Too broad to say. It would require more diagnosing. It also depends on how the waveform looks too

[@JoelAutomotiveInaction]

wow i am still impress. good job

[@freddensing1224]

great tip for those of us still using a single scope

[@Inkd_watkins]

Such great 👍🏻 information

[@morusaracing]

That's a good tip. Thanks for the video.

[@franciscodiez5825]

Awesome thanks for sharing the great tips!

[@Confirm_selection]

There should be a group similar to "AA" for tunnel-vision! 😉

[@gonzgarr1592]

i though you look for the mirror image of can high and can low ?

[@train4905]

brillint sir.

[@atiqkhan6683]

Great video We all learn something new everyday

[@georgedawsonjr450]

i have a question about this i have a 2013 Malibu 2.4 engine that keeps throwing can but code but the can high and low are good but it has a can high - and + now the can high - is so small it only 100mv wave form it looks like a squiggly line i can't seem to find out if this is bad. the cods are in air bag and restrain. i can't talk to the fuel pump or there other modules after the bcm. im stumped has anyone seen this before and what might i check to see whats going on it in the can high that keep coming up. the last time i scanned the car it said can bus A is off line.

[@gmak1n785]

Great video thanks dude

[@keltecshooter]

Outstanding.

[@Hajduk12]

Great video!

[@eduardosaenz9349]

Ive chased the goose but ive never caught him lol good stuff mankeep up ☝ the great work im learning a lot thanks for ur time man

[@optimusplayers610]

thanks for this video.