GM Class 2 Network Diagnosis Tips

Automotive network communication diagnosis can be overwhelming for some technicians. With videos like this, we hope to help tie up some loose ends you may have to help increase your efficiency and accuracy as a diagnostic technician.
In this video, Keith demonstrates how to properly identify which module has caused complete network failure on this 2003 Chevrolet Trailblazer.
By utilizing a convenient splice comb built into the vehicle, and single channel U-scope purchased from Aeswave.com , Keith was able to quickly identify which direction to travel next by isolating the module causing the network to be compromised. We thank you for watching and hope you enjoy!

[@alanw5879]

Man, the information you guys provide is priceless, if a tech has had some basic training, these videos can help so much with real world issues. Not just "this is how a piston moves".

[@JoesAutoElectric]

That is one nice thing about GM. They had the foresight to add a splice point to test CAN. That should be a standard thing for all makes and models. Great diagnosis and explanation.

[@SAAutoRepair]

Nice job Keith. Thanks for taking the time to put that together

[@tankabbot22]

Thanks for all the great videos Keith! I can't wait to attend some of your classes this year. Have a Happy New Year! Vito

[@turningwrenchesautorepairm5017]

Really clear and concise video. Great job !

[@halopersin]

Ive been missing trained by techs videos. Thanks for some more awesome content Keith.

[@PaulysAuto]

This video is excellent, thanks for the detailed explanation Keith! Great video!!!

[@Tony-rl2fr]

Excellent demonstration. I didn't even know there was such a beast as a SINGLE wire network! I learned a lot just from this one video. Thank you for an excellent learning experience 👍🏻

[@burtpilon1735]

Great video and wow you guys from TBT are crazy good thx for your time

[@movingupautodiagnostics8645]

Terrific video sir, thanks a lot. This gives some great direction

[@michaelnicholson9092]

Job well done Keith. Nice process and a great video. Thank you sir.

[@TrainedbyTechs]

Thanks Michael

[@lokyblack3379]

Excellent diagnostic process, thanks so much for the class, i appreciate a lot 👍🏻

[@DavidGutierrez-zi4dy]

EXCELLENT!! Congratulations. Great video.

[@mikefoster3547]

Excellent, thank you for sharing!

[@duanehall723]

Excellent troubleshooting ! Subscribed because of this video

[@pontiacsrule8761]

Excellent learning video. I haven't seen any videos on class 2 networks. Usually just the can-bus. Much appreciated

[@wyattoneable]

ASE wave has some cool stuff. That was a great visual when you added the pin connectors and the scope lit up.

[@RenegadesGarage]

Trained by Techs.. Awesome video. Nice job on explaining it. I just ordered the same scope from aeswave. Thanks for sharing it.

[@sollykhan2385]

AWESOME video, THANK you for sharing the knowledge, and please do post more great video's often, 🙂

[@baxrok2.]

Very efficient diagnosis. Thanks!

[@winekuhler1]

Thank you so much! I have had this same issue with a 2005 Yukon XL 4x4 5.3. Have not yet found the issue, but I'm gonna order the U-scope and I'm confident I can find the problem with your excellent video with perfect directions on how to find the problem. Thank you so much!!!!!!

[@RonaldGriegoyoda]

Great video Keith. One of the better videos I've seen diagnosing a network problem. I'll be sharing this video with my fellow technicians I work with. Thanks for the video Keith.

[@L1Training]

No problem, thanks!

[@Diagnosedan]

Great Video Keith! Thanks for sharing!

[@chrisroberds6076]

Great video Keith!

[@kellyr9388]

Nice case study Keith thanks.

[@fishonnelson2353]

Excellent troubleshooting Sir!!

[@mechanicandskills7215]

Absolutely brilliant method Thanks a bunch cheers !!

[@cru551010]

Excellent video. Thanks 👍 👍 👍

[@btnerual]

Thank you. Good information and explanation.

[@MitchsGold]

Great video. i have seen several AC panels get fried when installing a stereo. Wires fall into the top and short out on the circuit board. Bet it spiked the rear module on that one. Most customers will not admit that they saw a spark, or blew a fuse. Nice work.

[@fastone371]

Great information here!!! Thank you.

[@James-fs4rn]

👍 great stuff! Thanks for sharing my friend.

[@miltonscornertobylove5068]

I appreciate all your vids ty!

[@luisonate2678]

Very good example and explanation….

[@8power0]

Hello Keith great video , was wondering what's in that bag you had in the video could you please make a video on what's in the bag and why you use them . BIG THANKS AND PLEASE KEEP UP THE GREAT WORK .

[@exmotorsports]

Great information and tool demonstrations too Keith. New to your channel and a subscriber. Look forward to seeing more. Thanks for sharing the knowledge. 😎 🍻 Cheers Kevin B. Extreme Motorsports

[@markferraro5250]

great video thanks im digging that harness tool

[@prospexican]

great video, thank you for the tool tip from aeswave, just placed the order.

[@LiborioDavalos]

Great video Keith. I had the opportunity to be at class with you and other great technicians at MTD, And you shared this video. I really appreciate the time that you guys invest on your videos to help us improve our skills. The only doubt I have in this case study is could the rear HVAC module be logic locked bringing the network down? But I’m pretty sure you had that covered. Thank you again for the great work.

[@bigfootemobileauto9734]

Hey Luis, what do you mean by Logic Locked? Thanks, Doug

[@joelaplnski5394]

Nice, thanks, learned a lot!

[@naushadali95]

Great diagnosis.thanks

[@billyyoder8171]

Thank you Keith. Good job. Appreciate your videos. Do you have a part number or link to buy the break out leads you used in place of the comb?

[@manuellamas4747]

Awesome video

[@billrimmer5596]

That was super!! Finally starting to understand the concept that each wire or module adds or overlays another square wave onto the screen of your scope. The wires all basically come together. Am I right?

[@fisherheard7072]

Super helpful!

[@ptours99]

thanks i had no idea where to look for my problem

[@sureshbabu-fl5kx]

Thank you very much sir. use full video.

[@weloveups831]

Great job explaining. Are there vendors that repair these modules like they do instrument clusters and Abs modules?

[@juliogonzo2718]

Seems like a lot of guys can't even rewire a light pigtail. You will always have a job!

[@alitehrani3415]

Was great excellent teaching thanks a lot, The wires that you connected to comb from ase wave, will fit only to GM or any cars?

[@haywardsautomotive6156]

Nice diagnosis Keith and the AESWave PN is DECS-04 for the comb harness. It's not on their website yet to order it online but if they call they will take the order.

[@hxc7273]

Hayward's Automotive I typed it in the website and it came right up. Maybe they got a rush of people calling and decided to add it. Lol

[@haywardsautomotive6156]

Great...yea I told him it wasn't on the site and he said he would load it...that's fast! I bet they have a lot of people calling for it.

[@JesusMunoz-dw9ms]

excellent very helpful

[@weldingjunkie]

Fantastic video Keith voice over was great. What’s the name of that wire the drivability guys made and the probe you had on the end of the video on aux module? Thanks for this.. Jay

[@markthompson8537]

Great video, but never assume body will have a good ground. Body has a bad ground, the door hinge or door check will be a poor ground. Connect scope ground lead directly to battery ground post or your scope pattern may be poor regardless if the signal is bad or good.

[@midnightsnackrifice7676]

Loved tour video though

[@sandyande]

Brilliant Keith really enjoyed training session many thanks, sandy

[@billrimmer5596]

Hey Sandy. Any sunshine in Scotland? And I’m checking your vids too

[@sandyande]

Bill the summer here has been fantastic , the best since 1976!!!! but still not as good as california! hope your well, sandy

[@billrimmer5596]

sandy anderson I know u enjoy the sunshine. But we have had over 100 degrees with pretty high humidity. No fun. I do jump in the pool every morning. And the evenings r nice. I would like to enjoy Scotland for a while. Eventually I would miss So Calif.

[@sandyande]

Bill Rimmer we miss California, great place I shall return soon!!!

[@victorbeltran3075]

I see since this was uploaded years ago still great information clear explanation but whether I did not pay attention or I miss it what or were can we find that tool on used on this video thanks in advance?

[@billyyoder8171]

Oops. Should have read the comments below. Got the part number. Thank you.

[@midnightsnackrifice7676]

Just went after the network connector on 05 escalade..it was taped up to harness with a grey tape and super hard to get to. Thanks GM

[@tomduffy3605]

Keith, can this test be done with the vehicle off and the ignition on? My truck had the radio changed and is now reading unknown driver and will not stay running. It has many of the same symptoms as the trailblazer in the video ie no interior power. It will start but then shuts off after a couple seconds. 2004 silverado 2500 hd with the lly duramax. Thanks!

[@smms1276]

THANK,YOU 👍

[@rodvan-zeller6360]

Great video. Question: are all the modules on class 2 network both receivers and transmitters? If so, are they always transmitting or only when pinged? Thank you in advance for your answers.

[@bruceprigge5212]

Thanks!

[@carlbrandon8040]

Can a blower motor or other device on that auxillary hvac module pull it down like reference voltage does to other modules?

[@alitehrani3415]

Thanks was geat

[@joeclark8029]

Nice video.. I like how you go into detail on how things work. My question is that you said the pcm or bcm has to be hooked up to get that 7 volts but when you took the comb out you hooked up your leads one at a time and on the first one you probed into there was a 7 volt sqaure wave and that might not have beeb the bcm or pcm either. Could you explain what you ment and why you got the 7 volts on the first module you probed at comb.. If this makes sense to you what im saying

[@L1Training]

The first module I added was the PCM, but yes, you need to add either the PCM or the BCM first.

[@bigfootemobileauto9734]

Hey Kieth great presentation. I don’t quite get why you would have to add the P or BCM first and use every pin to hook up and watch on the scope. Wouldn’t it work the same to just test each one separately?

[@arthurfricchione6614]

Keith great video. Is that harness adapter just for GM vehicles or can it be used to do other testing. I own the U SCOPE and does it utilize the U SCOPES single channel connection point THANKS MUCH

[@L1Training]

I have used it for many unconventional uses! Call AESWave to order one, I do not think it is listed on there website.

[@haywardsautomotive6156]

AESWave PN is DECS-04 for the comb harness. It's not on their website yet to order it online but if they call they will take the order.

[@romeodiaz4790]

Thank you...

[@dtnel]

Want to get a little clarification on this one. IF one was to plug a breakout box and do this test the same way would we get the same result or does this comb affect the ability of the breakout box to be utilized and each channel be checked for activity one at a time without having to remove the dash panel and drop the OBD II plug from it's mount location. Not that it's a problem removing it from it's location. I also do understand that not everyone has a breakout box either. I did see another video as well, channel name hard if impossible to remember at this point. Anyways the person doing the video made a couple important comments about using the breakout box. First was being that as techs you never know what a customer did to the vehicle prior to receiving it that it could be a good suggested practice to use a B.O. box each time you connect that way you can always check for power and ground and the OBD port this having proper polarity and possibly preventing damage to rather expensive scan tools. Also it would enable the tech to check each network line without having to drop panels, creak necks around because you have the B.O. box installed this making the job possibly easier on the ol body. I'm sure some or many may chime in but please do so as each amount of information we get that's more clarified ultimately helps us all. Also is there vehicles that a B.O. box this will or won't work for and if so what would one look for to identify this capability when approaching this type of fork in the road. BTW love watching the T.B.T. videos and keep em coming!

[@JEKitchens]

I'd really like to learn more about the can bus systems namely how the ecu communicates with the bcm and subsequent modules

[@reelmilitia6975]

Ummm mind if I borrow that tool? lol. Wonder if they rent these. I have a 2006 sierra 4.8 and after I went over some tracks and it got extremely sluggish..engine light came on and got the U1000 code along with p0449 and p0106...ordered the MAP and EEV valve..Been messing with it for days. Any tips?

[@smarty2564]

hi, can u please provide a link where I can buy the scott connector upgrade kit. Thanks

[@jwilkers1]

Thanks for the information and for showcasing the uscope. Do you think the software on the uscope justifies buying it over a different mini 4 channel dso? I am trying to decide on a good scope given my limited experience it just seems like I would outgrow the uscope quickly but the software it has would be very helpful. Thank you for your videos I've been putting the information to use all the time.

[@L1Training]

Its definitely worth it, a new software update is coming out for it soon as well, more features will be added. I have played with the DSO201 version, its missing a lot of functionality vs the AESwave version. Jorge, Carlos and Team did great on improving the tool!

[@jwilkers1]

Keith Perkins thanks for the input I just got some hantek amp clamps and adapters to run on the shop's modis but I want my own stuff and the uscope looked like it was really easy to run and with the presets it looks like it has a lot of functionality. I've been all over the map on buying a scope from hantek to uscope to picoscope even looked at some bench type scopes. I think I'm just going to bite the bullet and pick one and use the crap out of it to just get lots of experience with it quickly.

[@bigfootemobileauto9734]

Wilkerson Auto just want to add that the Pico is the way to go, especially if you need more than one channel. The Snap-On is nice but definitely not as much functionality as the Pico! Doug

[@bigfootemobileauto9734]

Yeah I purchased the DSO to try it out and the connections it has are NOT as functionally adequate as the U-Scope. Wish it had two channels instead of just one. Doug

[@autotechtogo6290]

Are you positive that the PCM/BCM provide the 7 volt bias? Two people on IATN state that this not true.

[@philmanwarren3666]

where did you get little box and the wires you are useing ?

[@micksautoelectrics8750]

Great Video and presentation.. So the radio had nothing to do with the fault , If i tried explaining that to a customer ti wouldn`t go down too well :) :)

[@SMCmurphy1]

Can you provide the diagram for the splicepack? Going through similar issue.

[@jameybarisoff]

Now you need to open the module and look at the soldering joints and chips and see if you can fix it.

[@33798]

What's the name of the communication connectors near OBD port that Keith is inspecting

[@artdiaz9437]

Is the pin tool compatible with any other oscilloscope?

[@alvinybanez1006]

Bro what do you call the devixe you are using that color red? Thanks

[@georgedawsonjr450]

how do i find a problem on a 2013 Malibu can high negative. the car cod is can a off line. it seems to be in the air bag and restrain. its not shutting the vehicle down it runs very well but it causing all kinds of other problems. false readings on the temp sensor and things like that

[@nealblue6413]

Hello Keith, I'm a little late here. I have a couple of questions. 1- where are you hooking up the leads on your scope, #2 pin on the dlc and ground? 2- if the pcm and bcm supply the 7 volts, how do you check the system with them removed from the network? Did I miss something?

[@NewLevelAuto]

Hey Neal , I figure I will jump in and answer for you. Yes pin 2 at DLC and pin 4 or 5 for ground . Neither the BCM nor the PCM produce the 7 volts alone. ALL modules on the Class 2 network provide their own 0-7 communication. I hope that helps

[@rwrobs777]

Keith, Great video. I want to do a GM Class 2 troubleshooting video for the members on the C5 Corvette Forum but unfortunately 99.9 % of members don't even have a scan tool and certainly not a DSO...I don't want to use my Picoscope, Scan tool or Can test box because that's not how they will T/S this problem...with a DVOM you won't see a 0-7 volt square wave anyway so how would be the best way to T/S for these guys ??...the C5 has 2 Star Connectors near the BCM so I guess remove the comb from one Star and see if the car will start...I think all of these data bus issues will be either "no start" or crank and shut down"....DeFazio did a '98 no comm a while back... if the Star is removed and the car starts I guess they could de pin each module data line and 1 by one install a pin and then install the comb until the car won't start...OR maybe just pull the fuse or fuses from each module until it starts. Thanks !!

[@bigfootemobileauto9734]

Rob W. Hi Rob. Yeah one cannot do adequate testing without the proper equipment. Doug

[@rwrobs777]

Thanks Doug !!...I guess I won't even bother doing a video about the Class 2. And YES without the proper equipment "testing is futile"...LOL !!!~

[@dtnel]

Best thing is just let the Corvette drivers be Corvette drivers as they probably won't want to or don't have the patience to do this.

[@shaunsautorepairs5410]

So did changing the radio cause this or was it just coincidence?. What radio was put back in the car?

[@arthurfricchione8119]

Keith would that comb connector also be called a gateway the connector which Keith Defazio often references and is it found on most vehicles or just GM. THANKS IN ADVANCE Artie 👍

[@TrainedbyTechs]

No. A gateway is a central ECU/module that acts as a translator for multiple networks. It is the "hub" so to speak for network communications. A splice comb is simply a way to connect and/or isolate modules to one common network

[@arthurfricchione8119]

Thank you Keith For that Clarification 👍

[@richardcranium5839]

interesting how these all talk on one wire yet they dont step on each other

[@obdiipolice7186]

It is like computers, 0's and 1's... Binary code

[@SuperMarioDiagnostics]

I've been missing out, very slick tool. I went to aes wave and something is up with the website 🤔

[@antegas]

Like!!!!!

[@user-fe3cq1uc1x]

I always use break arm for ground

[@schwazelbacher]

What about the radio? Still removed? Interesting that the radio install caused the fault?

[@jmil6612]

Likely tied the class 2 wire to b+ or something else at the adapter harness causing damage to the hvac module, guess the othe modules were a little more robust

[@dtnel]

I guess I got lucky when I installed a aftermarket radio in my 04 Tahoe but I did get a security bypass interface that I installed with the radio at the same time. For some reason I feel i've watched this video before but then some or it seems new to me. Either way good info!

[@DEADDART]

Where can I find the diagram for sp205

[@manuellamas4747]

By the way. Was it a coincidence the radio issue replacement caused this module to fail.

[@mastertech1978]

U say 7 volts but your meter said 3.70volts ? Explain please

[@livingonadollar2882]

A backyard mechanic should not be on here But dammit I have a .5 parasitic draw And broke it down to the aftermarket radio And as it is a 05 GM style cluster I have a feeling the stock radio use to talk with it was off and on ..I am getting warmer anyways lol

[@UnreachableMike]

How is that connector called?

[@1fnjo790]

Think it was something like a 2nd Class Low CAN Sucking Rooster Comb or Something like that

[@1fnjo790]

Splice pack Connector

[@bwest-yq3uc]

Audio is real low...

[@embreesmith7613]

it's "micro-scope", not u-scope .. :)

[@just1lifexx11]

Its alot of thinking.. me as human being.. i get fix and forget about it... that stuff is not for heaven..

[@moparmatt5896]

Uhg i hate bus