I ran into the same thing with my AutoEnginuity scanner. Even though their site says that it will read the ABS/TC system with the GM enhanced parameters, it does not. The closest they come to a disclaimer is that not all systems are available on all cars.
The most common cause is an intermittent wheel speed sensor. The dealer can be a funny place for getting those read. When I took mine in, they tried to convince me that I had to leave the car as it would take a couple of hours to run a diagnostic on it.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.