Who'* ready for a story? Gear up:

So…I have a well-maintained 2015 Tahoe LTZ. About 6 months ago, the “Trailer Brake System” began intermittently throwing a warning at me during a drive (warning on, then turn off a few minutes later). Strangely, that problem seemed to disappear for about a month and then the “BIG PROBLEMS” began.

Out of nowhere, and intermittently, the car would throw a whole slew of driver assist errors. This included Stabilitrak, suspension, trailer brake, power steering (none—slightly different later, stay tuned), park assist, adaptive cruise, and possibly some others in forgetting. Took it to a trusted mechanic. First thing needed was a new battery, so swapped that. Car ran smoothly!…for a week. Then the same issues. Took it back. They determined it was a bunch of corroded connectors and wires. So, they cleaned them up. The car ran smoothly! …for a week. Then the same issues. Took it back. They determined it was more wires, some “harness,” and the trailer brake module. They replaced. The car ran smoothly! …for 450 miles. Then ALMOST the same issues (no Stabilitrak warning this time). Took it to the dealer. They said the negative wire from the battery was drawing too much power. They replaced it. Car ran smoothly! …for one day. Now I’m 450 miles from home, thousands of $ poorer, and I’m still in basically the same situation as I started in. Ugh.

The current errors displayed are suspension, trailer brake, adaptive cruise, and steering assist (at this point it will EITHER be “reduced” or none…no rhyme or reason as to which of this happens), and sometimes the park assist (the lane departure doesn’t display any warning but it also won’t work). The lights displayed IF the issues crop up are the parking brake, the ABS, and the traction control lights. With the exception of the park assist, all of the above will happen together or none of it will happen. I

t’* SUPER intermittent. Sometimes the car starts and there are zero issues. Sometimes it starts with all of the above. If that happens and I wait a 15-30 minutes and try again, it can work fine again. The only other weird things I’ve noticed are the sensor for day/night seems to not work as well when these issues are happening and the front proximity sensors seem to notice things that are not there (for example, when at a stoplight, it will display something being close when there’* nothing). These two seem things are “issues” if the above errors are present during a drive or not. No clue if this is related.

So, any ideas…??!

My guess: Ground loose, corroded, or rotted into oblivion.

It sounds like they aren't quite diagnosing by thoroughly understanding the wiring diagram and then checking performance of various parts and symptoms with a scanner . . . as was done in this video:
My guess: This is a rotted or otherwise bad ground, maybe even the same one as in this video.

Seriously, watch this video all the way through, then maybe point them or yourself (depending on your skill level) at the grounds, especially the one that Eric found in the video.

After the dealer replaces the modules and such and it still don't work they will then get the meters out and start working.

LOL no kidding.

That was excellent. Hoping I can show the mechanic this had have them proceed similarly. Thank you so much for sharing!

Please let us know how it turns out!

Update: it’* been with another dealership until yesterday (nearly 4 weeks). They first “reloaded” the modules, which didn’t solve things (fortunately, the problem recurred while they had the vehicle after “reloading”).

They then stated it was an issue with the battery after confirming they did a “full diagnosis” of the modules, ground(*), and various other cables to test “voltage drops,” replacing the battery, and repeating the process. Someone pointed me to this video ( ) which was helpful in me trying to understand what this dealer’* “diagnostic process’* looked like. They indicated their process mirrored the process of the guy in this video, but…

Anyway, they replaced the battery and said “we’ll see.” None of this sounded encouraging to me, but I decided to pick it up yesterday. What happens today? Same exact thing! Woohoo! Back to step one.

Did they inspect grounds like in the video?

Did they take pictures?

They assured me they tested the ground in the video (I actually asked that they just replace it just in case—“no, no, we tested it and it’* fine.”). I think the extra tricky bit is that the issue doesn’t come and go like in the video. It’* either present and won’t go away (until it does…) or it’* not an issue and one can’t produce the issue on demand (by running a bunch of auxiliary stuff or turning the wheels).

I had a good chat with my first mechanic—they spent some time watching the video, “learned a couple things,” and want to take another stab. I feel good about what they relayed, so I think I’ll take it back there before returning to the dealer.

Here'* the thing with the testing they did as I understand it. If they simply tested for a ground path, a worn out, almost failed, corroded, awful ground will still show a ground path. If something has a higher current draw than a meter doing a continuity test, the worn out, almost failed, corroded, awful ground will create extra resistance, current won't flow, and interesting things will happen. Everything in your car uses more power than a continuity test on a meter. Sometimes there'* no replacement for physical inspections.

Looking forward to hearing what the mechanic finds!