GMC Envoy intermittent no start Class 2 fault

This GMC Envoy had an intermittent no start. Come along as we diagnose the no start. We quickly realize the data network is down since we cannot communicate with any modules. This vehicle uses GM Class 2 communication on a single wire.
By scoping the network on pin 2 of the data link connector we see that the network is getting shorted to power. This is causing the no start condition since the modules cannot confirm security information and starting requirements.
Many of these Class 2 vehicles have convenient network splice packs that allow us to isolate modules on the network without unplugging all the modules one at a time.
After working our way through 2 splice packs we isolate the liftgate module as the cause of the communication fault. Broken wires in the decklid harness caused lot of grief and a wild goose chase.
thanks for watching

[@nickstaropoli9618]

Thought you did a great job most people have no idea how hard wiring can be thanks

[@theGADGETSplaylist]

intermittent no start with broken wires in the trunk there's no direct path to that without a few detours along the way you got there and fixed it as good as it gets Chad:)

[@spelunkerd]

Brilliant video, Chad. I love the way those splice packs save diagnostic time. Your explanations are perfectly gauged to my skill set, thank you!

[@brandonjoseph8608]

Good reminder of the can buss. I've been searching though the starter wiring. Thanks I'm confident I'll find the problem now.

[@lokyblack3379]

Excellent process of diagnostic 👍🏻

[@rodvan-zeller6360]

At 18:20. Be nice to yourself you did a great job. Do the easiest first and keep going.

[@cinorom3803]

haaaa! I went straight to this video (actually the 2nd one I watched) but great info. Thank You!!!

[@nelsonnarciso1791]

Well done brother. These can be very hard to find

[@High_Tech_Mountain]

Chad brother! Miss your videos. Have a few to catch up on. The importance of having more than 1 service information!! As much of a pain it could be getting to the splice packs.. it beats going to modules one by one and unplugging. && lastly.. I like ‘em when they’re without a doubt BROKEN! The intermittents are no fun As always great video and thanks for bringing us along

[@ThePracticalMechanic]

Thanks for watching Angel. Everyday I find more and more holes in each service information provider. It’s getting old. The scan tools are getting more and more holes as well. I had a Lexus that would only act up 2 times a year and after looking at it several different times I finally figured out what was causing the issue and the customer declined. I’m hoping they change their mind so I can film it.

[@exmotorsports]

@@ThePracticalMechanic Oh Man....I'm sure that would be a great one to see.. Hope you get that opportunity bro

[@weldingjunkie]

Good to see a video for me Chad miss watching you guys. Hope all is well, I would’ve definitely unplugged each module out of habit

[@ThePracticalMechanic]

I default to module unplugging because of all the issues I’ve had a Chrysler over the years. I wish all vehicles had the spice packs like this one had. It would make isolating the bad module much easier.

[@LuisEscobar-l6r]

Thank you for such a detailed video. You rock man!!

[@lornafulsom21]

Im sitting in my car with it refusing to start - the ignition doesnt seem to connect + although it seems tohave power. We tried to jump it but my friend said you have power to everything so its wierd. Just random all of a sudden I ve only had the car a month and everything was good or recently done (beaides needing a new cluster which i new and found at a pick and pull to go maybe pock this weekend) so Before calling a tow truck i goggled the issue to see if it was related to cluster and found you. Im hoping it might start again if i leave it over night to get me to a shop tomorrow and im going to recommend to them yr video. Hopefully i can afford to fix it all now thst you sepent the investigation time. Thank you

[@philh9238]

That was a good case study. Honestly if there’s a splice pack that’s where I go. Especially on the newer Chrysler’s where they have the star connectors. Oldie communication network but good diag

[@ThePracticalMechanic]

In Colorado I don’t see comm networks go down often so I am normally out of practice. The guys on the east coast seem to get most of them.

[@nickayivor8432]

ACCOMPLISHED The Practical Mechanic My teacher Thank you very much for sharing what you know with us information video was very helpful take care and have a great Evening with all your family around you ACCOMPLISHED The Practical Mechanic From Nick Ayivor from London England UK 🇬🇧

[@exmotorsports]

Hmm.. What would have I done differently you ask.? Well, I would have pulled up KZbin and watched your video.! 😂🤣 I would have probably had that seat torn apart and on fire just from the frustration itself. Lol Ok, maybe not, but it has crossed the mind a time or three. Lol Honestly, don't think I would have done anything much differently Bro. Great job my friend 👍

[@ThePracticalMechanic]

Ha! Thanks Kevin. Funny thing is I have seen three of these since I made this video. Two came into our shop and one was a mobile pcm programming where I had no communication and couldn’t program the new PCM. I told the shop what to check for and they repaired it before I came back to complete the programming. They had already sent the original PCM back as a core a week before they called me in to program.

[@turningwrenchesautorepairm5017]

Good case study

[@ThePracticalMechanic]

Thank you. I just ran into this on another vehicle. Shop called me out to program a new pcm and I couldn’t communicate with any module on the network. They also had a battery drain sometimes. I didn’t have time look into during that visit so the shop dug into it and found the lift gate module causing the issue. When I return I pulled back the boot and found all but two wires broken through. Repaired the wires and programmed the pcm. They had already sent back the core so we couldn’t test if the original pcm would work. I guess the original had some other intermittent issues as well so it may have needed it. 🤷‍♂️

[@turningwrenchesautorepairm5017]

@@ThePracticalMechanic I do not see a whole lot of comm failures. So seeing another tech walk me through the process is great help. Thxs again buddy

[@johnphillips1001]

Excellent video 😊😊

[@shamessun]

good job and good video. thank you

[@jakemartin4305]

I would have just jumped to modules that splice pack trick is a great idea and i dont think you could have done anything different and that seat bugging out would have gotten anyone confused

[@nickayivor8432]

SUBSTANTIAL The Practical Mechanic Questions time Pete Meier Motor Age Would have done Voltage drop testing to trace fault in the wire harness SUBSTANTIAL The Practical Mechanic Thank you From Nick Ayivor from London England UK 🇬🇧

[@georgebonney90]

Thank you sir

[@waynetaylor7086]

PICTURE QUALITY SEEMS NOT FOCUSED BUT GOOD JOB

[@Nobody_Yuno]

Ive had about a half dozen of these and every one has had broken wires in that pass through in back. the key FOB module is in the hatch. i also repair the four or five body grounds under the hood as they are usually terminals to painted surfaces and have poor continuity from the factory.

[@lacaninicastro]

awesome

[@ErnieMoubray]

I'm having the same problem it was running good in way to work it shut off on me and would not start again put scan tool on it,code ignition switch fault 2and rear wheel speed sensor,so I'm going with your aproach,owners before us put electric start on it and it's in that first splice pack u touched front dash

[@martinarrieta248]

Grasias

[@ThePracticalMechanic]

Thanks for watching

[@jgeorges3061]

Great video/information and while you where checking the signal from splice pack you used the wire that was on pin 2 or not brother and as always learning from the best thanks for sharing.

[@ThePracticalMechanic]

Yes I just moved my test lead from pin 2 on the DLC to the splice pack. I hope the next one will be easier for me to diagnose but by time I see another issue like this I will likely forget to just jump to the splice pack. I just ordered the Uisolate test leads from AESwave. it allows you to connect to all pins of the splice pack and then you can unplug one at a time to find which wire is causing the issue. www.aeswave.com/cart.php?m=product_detail&p=9669&lastAddedItemId=398217

[@seandarrah3603]

Did this cause unknown driver warning on dash?!

[@yousifmorsy6511]

Please give a link to where I can find wiring diagrams of trailblazer 2009

[@ThePracticalMechanic]

eautorepair.adtrk.biz/?a=10863&c=10032&p=r&s1=

[@yousifmorsy6511]

Thanks

[@yousifmorsy6511]

Unfortunately it's not free download!!

[@ZareefHuq]

I know it's been a while since you made this video, but I'm having similar class 2 failure issues on my Envoy. I had a question, even with this class 2 failure, were you able to operate the liftgate lock and rear wiper still?

[@ThePracticalMechanic]

I don’t remember but my guess would be that the lift gate would still open since I had to open it up for repair. With the number of broken wires in the hinge it’s possible to have functions acting up as well.

[@ZareefHuq]

@@ThePracticalMechanic thank you! A follow up question if you're able to remember, but were all the dash lights coming on or just some of them? None of my dash lights come on except the CEL (powered by the ECM) and the battery light (powered by ignition fuse). A scan tool can get the high beam and passlock lights to come on, and sweep the gauges, but that's it.

[@screamingflat6]

Good video, did you buy the Zeus plus yet?

[@ThePracticalMechanic]

Thanks Jeff, I don’t see the need to upgrade from my current Zeus at this time. My dealer is on vacation until next week so I have not seen the + in person yet.

[@mike-yp1uk]

Oh yeah you just gotta love fixing cars because why else would anyone torture themselves. Lol