Although manufacturers have different names for it, the mechanism is generally the same: It makes sure individual wheels automatically break to prevent the vehicle from over-steering or under-steering, says Achmed Leser of the German Association for Technical Inspection.
"Sometimes, it directly affects the engine control as well, which is even quicker than intervening with the breaks," Leser says.
All this helps prevent the car from spinning or swinging off the road in extreme situations. Here is how it works:
Interfering with the steering process
"The most up-to-date systems even interfere with the steering process and additionally support the driver to stay in their lane," the expert says.
To be activated in the right moment, the system permanently monitors signals from different sensors. Comparing wheel speed, steer angle and yaw rate can for instance help detect unstable driving conditions in the fractions of a second.
If the controller detects a different driving behaviour than that prescribed by the driver, it immediately interferes and holds the car in the correct lane as long as physically possible, Leser says.
"Of course there are still situations in which even a highly modern ESP can't help anymore," the expert adds.
One click to turn it off - why?
But why can you deactivate the ESP at the click of a button in some cars? Some manufacturers offer different driving modes, including a sports mode, Leser says. "That shifts the rules threshold for the systems and the interferences happen a little later," Leser says.
But only few vehicles let you turn it off completely these days. Some systems merely let you turn off the traction control system, which prevents wheelspin. This can be useful for example when starting the car on slippery ground, Leser says.
ESP systems were invented by the German manufacturer Bosch in 1995, but were initially only put into expensive high-end vehicles.
But when a car overturned in 1997 after having tried to dodge a moose on the road, the case for building the ESP into all vehicles grew stronger.
However, it took almost 20 years for the system to become mandatory. In 2014, the European Union decreed that every new car has to have it.
Nonetheless, between 2000 and 2013 alone the ESP saved some 6,000 lives and prevented around 200,000 accidents in Germany, according to the German Insurers Accident Research.
