When the ABS light is on the computer has turned that safety feature off so all you'll have is standard brakes. By far the most common cause on GM front-wheel-drive cars is a little normal play develops in the front wheel bearings that lets the signals from the wheel speed sensors drop out. That typical results in false activation at low speeds. If your yellow ABS light comes on as soon as you start the engine, it is most likely an electrical-related problem like a broken wire to a wheel speed sensor. Your mechanic will read the stored diagnostic fault code to determine the circuit or system that needs further diagnosis.