ESP

What is the ESP (Electronic Stability Program)?

ESP, an acronym for Electronic Stability Program, is an active automotive safety system translated in French as Correcteur Électronique de Trajectoire. Having become an essential standard, this intelligent system acts as an electronic guardian angel, ensuring that the vehicle maintains the trajectory intended by the driver, even in difficult conditions. Its primary objective is to prevent losses of control, whether it is a skid in a corner or a sudden avoidance maneuver. Since November 1, 2014, ESP has been mandatory on all new cars sold within the European Union, highlighting its crucial importance in reducing road accidents.

How does the Electronic Stability Program work?

The operation of the ESP relies on a constant analysis of the situation by a central computer. It collects information from several sensors strategically placed in the vehicle:

• Steering angle sensor: it informs the system of the direction desired by the driver.
• Wheel speed sensors: identical to those of the ABS, they measure the rotation speed of each wheel.
• Yaw rate sensor: it measures the rotational movement of the vehicle around its vertical axis (rotation/yaw).
• Lateral acceleration sensor: it detects the lateral forces experienced by the car, typical of a cornering maneuver or a skid.

By comparing the driver's intention (steering angle) with the actual behavior of the vehicle (yaw and acceleration data) hundreds of times per second, the ESP detects the slightest sign of a skid. In the event of a discrepancy, it intervenes instantly by applying targeted braking force to one or more wheels, and can also reduce engine torque. For example, in the event of understeer (the front axle slides toward the outside of the turn), the ESP will brake the inner rear wheel to help the vehicle pivot and regain its trajectory. In the event of oversteer (the rear of the vehicle slides out), it will brake the outer front wheel to stabilize the car.

ESP, ABS, ASR: What are the differences?

These three systems are often confused, but they have distinct and complementary roles, with ESP being the most advanced of the three.

• ABS (Anti-lock Braking System): It prevents the wheels from locking up during heavy braking, allowing the driver to maintain steering control to avoid an obstacle. ABS is an essential technological building block for ESP operation.
• ASR (Anti-Slip Regulation or Traction Control): It prevents drive wheel slip during acceleration on low-grip surfaces (rain, snow, gravel). It acts either by braking the slipping wheel or by reducing engine power.
• ESP: It goes further by managing the lateral stability of the vehicle. It uses the components of the ABS and ASR to correct the overall trajectory of the car and not just to manage braking or acceleration in a straight line.

Can ESP be deactivated?

Most vehicles equipped with ESP have a button to deactivate it, often labeled "ESP OFF" or featuring a skidding car symbol. However, doing so is strongly discouraged under normal driving conditions. Deactivation can be useful in very specific situations, such as starting in deep snow or mud, where slight wheel slip can help find traction. On some sports cars, a "Sport" mode may relax the ESP intervention to allow for more dynamic track driving, but the system generally remains on standby to intervene in the event of a major loss of control. In the majority of cases, the system reactivates automatically above a certain speed (often 50 km/h) or when restarting the engine.