I believe you mean in addition to the Trac Off and ABS lights, your Service VEHICLE Soon light is on. The Alero's have both: a Service Engine Soon light and a Service Vehicle Soon light. With the three lights you're talking about, have a bad wheel bearing or speed sensor at one of the wheels. Once you figure out which wheel the fault is coming from, you will need to replace the entire hub assembly.
I'm not sure exactly how to locate which wheel the fault is at, but maybe some of the other guys can help you out. The only way that I know is to hook it up to a GM scan tool. When my speed sensor went out, my car was still under warranty. The dealership pulled a code that said "excessive right front wheel spin". If you have a bad speed sensor, the code that your car will have logged will be similar to that.
- Jeremy