The Electronic Traction System Intervenes if one of the drive wheels begins to spin. In contrast to the automatic locking differential (ASD), ETS is active over a wider speed range. Brake pressure is applied specifically to the spinning wheel, so improving traction.
The system intervenes at speeds up to 40 km/h//25 mph and during acceleration remains activated up to 80 km/h//50 mph. During extremely long braking operations the ETS shuts off automatically to prevent overheating of the brakes.
Mercedes-Benz M-Class 4ETS system