MY 97 GC ABS light is always turning on. The mechanic tested the ABS brakes twice and determined that the ABS sensor was bad. However, the light keeps coming back on (now at least not constant). Any ideas?

Usally if a wheel sensor is bad the ABS Light will come on once the vechile is moving. If it comes on as soon as you start up it is more serious -pump accumulators. Iam assuming the mechanic ran a scan to retrieve the codes on the system. The ABS System sets a code just like the ECM does. You need a Scan Tool that will read the ABS System to help with the Diagnostic process.