ESP (Electronic Stability Program)

ESP is a system that assists the driver in stabilizing the vehicle in unexpected situations that would otherwise could be difficult to handle by regulating engine torque and brake application.

The ESP, ABS and TCS functions work both independently and in combination with the same control module. Certain functions may operate despite a lit ESP OFF warning lamp.

When ESP engages due to a skid, for example, it can counter the skid by applying the brakes on one or more wheels without the driver having to touch the brake pedal. The engine power is also limited by the ESP control module requesting a certain engine torque to reduce the risk of spin on the drive wheels. The engine control module regulates the engine torque based on this request. ESP regulates instantaneously at high frequency according to the prevailing conditions.

The system receives information from a number of sensors and measures:

• Wheel speed
• Lateral acceleration
• Yaw rate
• Steering wheel angle
• Brake pressure

These values are used by the ESP control module that is integrated in the hydraulic unit. The control module calculates the course of the vehicle continuously and compares the actual value  (the direction in which the vehicle is travelling) with the desired value  (the direction the driver has chosen with the steering wheel).

If the actual value does not agree with the desired value, the system will engage as necessary to apply the brakes on one or more wheels and limit engine torque.

• If the car starts to understeer  (when the front tends to continue straight ahead in a bend), the brakes will be applied on the inside rear wheel.
• If the car starts to oversteer  (the rear tends to drift out), the system will apply the brakes on the outside wheels until the measured and the calculated yaw rates correspond.