The traction control attempts to control the wheelspin, usually by applying an individual wheel's brake (or both, as necessary). It does this through ABS modulation, so it'll have a rumbling sound as it's doing it. It should also display "TRACTION ENGAGED" on the DIC (the Driver Information Center). This is the message to you to not get alarmed, the car is simply doing its job.
The traction control can also request a torque modification from the engine, where it cuts certain cylinders, but this is in a severe situation where the brakes have been overheated (the ABS "guesses" at the temperature of the pads as it applies the brakes -- the newer models actually have temperature sensors at the pads I think). Again, the traction control system
only requests a torque modification from the engine after it thinks the brakes are over worked. In other words, it'd be hard to do this. Maybe if you sat on ice and spun them for 10 minutes straight or something. Or maybe a severe case of rocking the car, trying to get it out of snow. But normally, you would never have that happen to you (torque reduction).
Another note -- if there is no wheelspin, the traction control does not engage. Period. How would it know to engage...and what would it be controlling if there were no wheelspin? It's actually fairly liberal -- it will allow up to about 10% wheelspin. You can chirp the tires and scuff them a little bit during acceleration without the traction control activating. Check it out on dry pavement. Practice a little bit with it. If you floor it right out, you'll probably spin them outright, and activate the traction control. But with practice, you'll get the tires to chirp or squeak off the line and you zoom away, with nary a "TRACTION ENGAGED" message on your DIC.
