The Traction Control Unit is activated when engine torque and throttle input are not matching up. This means that the amount of power the engine is putting into it is not the equivalent to what it’s getting out of it. Now a days it’s usually integrated into anti-lock brakes meaning they share the same computer systems. If the sensors are tripped the car applies the brakes to wheels that are slipping. This initially slows the car until traction returns to the wheels thus stabilizing the car.