Service traction control light
I checked powers and grounds at ebcm with 4 amp headlight bulb. I have 60 ohms resistance on pin 6 and 14 on dlc. Need some direction on what I should test or check. I will try to load a file of the communications while the fault happens . I tried hitting hard bumps in roads Moving harness in engine bay and around bcm and no service traction control light. Only when you rev the engine and its intermittent. No apparent damage on harness that I can see.
Didn't mention that on top but yes I was thinking the same but wave form was good . I tested it at idle with no loads or under acceleration not sure if that would change the outcome of the ripple test
Off-the-cuff I would say check for alternator ripple, and check for excessive noise from a (bad) ignition coil.
How would I check the noise coming off a coil. Is it the control wire going into the coil or use an ignition pickup clamp on the spark plug wire.
Scope the grounds, zoomed-in, and look for a huge spike that mirrors an ignition event. Some noise is OK/normal but see if you see a huge spike before the MIL sets. That EMI will be everywhere under the hood. Many stories of one bad coil causing crazy issues, maybe yours is another one. This is not quite your issue, but I made a short video the other day about watching the grounds to find a missing ignition event; youtube.com/watch?v=MUr2YD…
I am not sure what the definition is of that code, but I see it is a communication code. I have learned that when there is a CAN communication bus problem.... the first distant early warning telltale to the driver will be the TRAC light or traction disabled message on dash. Then you may find U codes in one or more modules, and the problem can be kinda anywhere on the network, not specifically where the codes are stored in and so on. What may be helpful is to use the GM BUS Diagnostic tool, drive around until the problem presents itself then quickly look at the modules reported as being online, compare that list against one when there is no problem currently present. This can give you an idea as to where a break in the network is occurring.
are all 3 trucks fleet vehicles?
Do they have any tracking or data monitoring components connected to the communications busses?
any other drivability symtoms present when the fault occurs?
The IPC will turn on the traction warning lamp if it stops hearing from the EBCM. The EBCM is giving a clue with the loss of comm code. Being as this is a fleet vehicle there maybe something added for data recording or fuel/speed limiting gone awry that is interrupting state of health messages between modules. EMI from another failing electrical component such as alternator or other add on acessories are possible culprits
I have a factory scan tool on the way tomorrow to check on what module or modules come offline when. The light comes on. All three trucks are fleet trucks . I removed the GPS fuses off one to make sure and problem still persist . The GPS was tied into the fuse box in engine bay and not connected to the dlc . But since pulling a fuse is easy tried it anyway and no dice on the GPS being the culprit. The only symptoms I can say is happening is shifting becomes delayed when fault happens on acceleration. But I can also make the fault happen in park feathering the pedal around 1,200 to 2,000 rpm. Not always but I can eventually get it to trigger like that. And more success recreating while in motion under acceleration.