ABS system is overreacting...
 

I have a 2001 Monte Carlo 3.4...the last week or so the ABS system has been activating at random while braking, even during extremely mild braking. I was slowing to pull into my driveway the other day and the ABS system went off. My fiancee normally drives the car, and she said that it's been happening quite often when she's just driving around and braking normally, and that every now and then the Service Traction Control indication will be tripped on the information screen, and the ABS light will turn on, but it always resets itself when you restart the car. I pulled the OBDII codes and there wasn't anything there related to any of that, just a couple other known issues (O2 sensor error and a persistent low coolant temperature reading even after replacing the thermostat and temp sensor).

Is there a common sensor that would fix this, or will I have to take it to a shop and have them diagnose which wheel is throwing a bad speed reading? I can't imagine that'd be cheap. :(

The speed sensors for the wheels are in the wheel hubs. Odds are one has gone bad. I believe to read the ABS data, you need a different scan tool (this OBDII scanner I don't think does anything with ABS).

I had a couple of cars causing some serious ABS problems (uncontrolled braking type problems, almost ending in collision). Those problems frustrated me so much, I popped the wires off the master break cylinder to disable the ABS system until I could solve it (those were mid-90's cars).