Problem With '99 Cavalier Z24 ("Low Trac" light ocmes on a few times hten "ETS" and "ABS" are disabled)

OK, here's a puzzler that I can't get figured out. Maybe someone here knows something. I'll try to list all the facts and cause/effects I see.
Last year, around October, I had a service done on the car. Highly
recommended and good rep shop. They also rotated the tires. The tires are near new, about 15K on them and still not showing any signs of wear.
On the drive home I noticed the "Low Trac" (Low Traction) light come on, which I thought was odd because the road was dry. It came on again 2-3 times and then there was a clicking sound like when the ABS kicks in and the ABS and ETS (Electronic Traction System) lights came on (means they are disabled). I'd been driving the car for about 3-4 months and never seen this happen before. Anyway, I had stopped at a light so I turned the car of and restarted it ('reboot' if in doubt!) and it didn't happen again on the ride home so I thought no big deal.
However, for the next 2-3 months at random intervals this sequence would repeat itself -- Low Trac light comes on 3-4 times in a 1-3 minutes interval and then the ABS clciks and the ETS and ABS lights come on and are disabled. Sometimes this happened when I was on the road and the road surface was suspect. I called the shop and told them it happened right after they rotated the tires, took it in, but couldn't repeat the problem (totally random). Then my battery and alternator needed replacing and I noticed that after that the problem never repeated.
The car went in for an oil change and general winter checkup back in Dec, and yup, they rotated the tires, and the problem came back. I have underground parking and if I start my car and a second or two later the Low Trac light comes on (I'm stationary!) I know that the ABS and ETS will disable before I can even get outside. I usually turn the car off and restart before I leave the garage. About 50% of the time this solves the problem for that trip. It also happens when I turn tightly, especially a left turn at low speed (like in my parking garage).The problem occurs more often when it's really cold (it's been -40C lately!) and the car has been parked outside overnight and now the ETS/ABS will disable without even the ABS click sound that tells me it's about to disable.
Now, to me this is a problem with a sensor or something on one or more of the tires. I'm assuming that the "Low Trac" shouldn't come on when you're stationary on dry ground or moving on dry, clean ground. The problem is that in these kind of road conditions I like having my ABS and ETS working, but not knowing if they're working unless I glance at the panel and see the light is another layer to deal with in a situation. I thought of disconnecting the battery and seeing if that solves the problem but I don't know what else that might screw up (if anything). I'd like to go back to the shop and get it resolved, but I want to know I've done everything I can before I do that (it's way across the city and I'm so busy I can't give up a day without my car).
Any ideas? Any suggestions?
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Get the ABS error codes read. The last time a car of mine did that, it turned out to be a wheel hub.
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Try getting it on a OBC scanner and see if any codes are set. If you have problem with one of your wheel sensors it should show up.

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Like the other two replies, get the codes read.
Remember: 1. Light comes on. 2. Read codes. 3. Test drive. 4. Light comes on. 5. Read codes. 6. Diagnose. 7. Repair.
I'm not sure how fast of a typer you are, but that was a lot of words. Too many for my to read but I got the gist of it: lights came on and I didn't notice any DTCs whilst skimming. ;)
Steve
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