Any GM Certified Master Tech Familiar With GDS2/MDI Functions?

[Doubeleive]

I have some questions regarding can bus errors that keep popping up and communication errors
if anyone is interested I am trying to narrow the problem down to either the BCM or can-bus communications or both.
on my 2018 Silverado I get
radio codes only no HMI codes
u0028 most bus
u0140 lost communication with bcm
u0164 lost communication hvac
b1325 high voltage
ebcm codes
u0126 lost communication steering wheel angle sensor
u0151 lost communication inflatable restraint system
u0077 control module communication can-bus
I can clear all the codes from history, sit there and scan it on the same session and get no codes
drive it a little bit turn it on /off scan again
little by little within a few minutes the codes creep back one or two at time
all will come up as either history or passed and failed
no open code
on different sessions I loose complete communication with radio and most of the modules, while those communications are down the ebcm is flagged and serial data gateway module is flagged, hmi is green, bcm is green and power steering control & transfer case module is green

the dealer is hesitant to do anything because i have aftermarket equipment installed such as a alarm system, hid lights, led lights

here are a couple photo's showing how I get intermittent communication, works and then it doesn't work

vehicle has no cel, drives and runs great, radio gives me intermittent problems, but these other codes are unrelated and should not even be coming up

 

[swathdiver]

Repeat this post here too Wes: https://www.gm-trucks.com/forums/forum/81-ask-the-gm-technician/

 

[Tiredmechanic23]

While its not a vehicle I do deal with can-bus systems on heavy equipment. Normally when I see a ton of errors relating to module communication its intermittent power/ground issues. Usually a bolted down ground somewhere has gone bad, a chaffed power wire, chaffed can wires or a dirty/loose connector. Having never had the dash out of one of these things to get a good look at everything I would be unsure if there might be a spot where the harness is pulling on itself at a connector or not. In the world of heavy equipment that seems common to let a connector hold up 10lbs of harness...

My wifes journey though did have a bunch of can errors similar to what you are seeing and I found a chaffed ribbon cable to her roof mounted rear screen.

 

[Doubeleive]

While its not a vehicle I do deal with can-bus systems on heavy equipment. Normally when I see a ton of errors relating to module communication its intermittent power/ground issues. Usually a bolted down ground somewhere has gone bad, a chaffed power wire, chaffed can wires or a dirty/loose connector. Having never had the dash out of one of these things to get a good look at everything I would be unsure if there might be a spot where the harness is pulling on itself at a connector or not. In the world of heavy equipment that seems common to let a connector hold up 10lbs of harness...

My wifes journey though did have a bunch of can errors similar to what you are seeing and I found a chaffed ribbon cable to her roof mounted rear screen.

I poked around on the gm techlink website the other day and found some common places to look for broken or chafed wires and I jacked it up Sunday afternoon and got under with my flashlight and poked around but couldn't find anything that looked obvious, wish I had a lift that should make things easier I got my creeper out and checked everything I could see or feel. Then yesterday I hooked the scanner up and drove around and tried to monitor various modules to see if I got any voltage spikes or anything nothing evident there, I pulled out part of the back seat because I had been back there installing a couple amps not long ago and though maybe I knicked a wire or something but couldn't find anything there either. It's getting a 4 1/2" lift kit put on Friday so it's going from being lowered to lifted maybe I will be able to see something then. I did pinch a abs wire when it bottomed out on a speedbump but I already replaced that, just chasing a ghost right now.

 

[Doubeleive]

@Tiredmechanic23 have you ever used a obd breakout box, I have seen them online I wonder if that might help me find the culprit

 

[Tiredmechanic23]

@Tiredmechanic23 have you ever used a obd breakout box, I have seen them online I wonder if that might help me find the culprit

I have not but I have thought about getting one myself to use with my Modus scope functions. I figured I could see how much I liked it then possibly build or buy one if possible for the equipment I work on.

 

[Doubeleive]

just a update to this thread, discovered the alternator was defective and was sending voltage spikes to the bcm causing the ignition to restart, this caused multiple modules to have a bad handshake, problem seems to be resolved with a new alternator.