Description and Operation

ESP Description

Optimum driving safety now has a name: ESP, Electronic Stability Program. ESP recognizes critical driving conditions, such as panic reactions in hazardous situations, and stabilizes the vehicle by individual wheel braking and intervention in engine control without the need for the driver to depress the brake or accelerator pedal. ESP adds an additional function known as Active Yaw Control (AYC) to the functions of ABS, TCS, EBD and ESP. While the ABS/TCS function controls wheel slip during braking and acceleration and thus mainly intervenes in the longitudinal dynamics of the vehicle, Active Yaw Control stabilizes the vehicle about its vertical axis. This is achieved by individual wheel braking and adaptation of the instantaneous engine torque without any action required by the driver. ESP mainly consists of three components: sensors, electronic control unit and actuators. Naturally, the stability control function operates under all driving and operating conditions. Under certain driving conditions, the ABS/TCS function may be activated simultaneously with the ESP function at the driver's request. If the stability control function fails, the basic safety function, ABS, continues to operate.

ESP Control Description. The ESP system includes the ABS/EBD, TCS and AYC (Active Yaw Control) functions. ABS/EBD function: The ECU converts the analog sensor signal (current offset) received from the four wheel sensors into a square waveform. Using the input of the above signals, the ECU calculates the vehicle speed and the acceleration and deceleration of the four wheels. The ECU determines whether the ABS/EBD system should be activated or not. TCS function: Prevents wheel slip in the driving direction by adding brake pressure and reducing engine torque via CAN communication. TCS uses the wheel speed sensor signal to determine wheel slip, as with the ABS function. AYC function: Prevents unstable vehicle maneuvering. To determine vehicle maneuvers, the AYC function uses maneuver sensor signals (yaw rate sensor, lateral acceleration sensor, steering wheel angle sensor). If the vehicle maneuver is unstable (oversteer or understeer), the AYC function applies brake pressure to the specific wheel and sends an engine torque reduction signal via CAN. After the ignition is turned on, the ECU continuously diagnoses the system for malfunctions (self-diagnosis). If a system malfunction is detected, the ECU informs the driver of the system failure through the BRAKE/ABS/ESP warning lamp (fail-safe warning).

Variant Coding. The HECU is programmed with a variant code based on the vehicle's powertrain configuration. This variant code is used to determine the appropriate ESP calculations. Variant code programming must be performed whenever the HECU is replaced.

Input and Output Diagram

ESP Operation Mode

1. 1
   STEP 1: ESP analyzes the driver's intention.

   

2. 2
   STEP 2: It analyzes the vehicle motion with ESP.

   

3. 3
   STEP 3: The HECU calculates the required strategy, then activates the corresponding valves and sends torque control requests via CAN to maintain vehicle stability.
4. 4
   ESP not operating — normal braking.

   	Inlet Valve (IV)	Outlet Valve (OV)	Traction Control Valve (TCV)	High Pressure Switching Valve (HSV)	Return Pump
   Normal Braking	Open	Close	Open	Close	OFF

   
   

   

5. 5
   ESP Pressure Increase Mode

   	Inlet Valve (IV)	Outlet Valve (OV)	Traction Control Valve (TCV)	High Pressure Switching Valve (HSV)	Return Pump
   Normal Braking	Open	Close	Closed (Partially)	Open	ON (engine speed control)

   
   

   

6. 6
   ESP Pressure Hold Mode (controlled only for FR)

   	Inlet Valve (IV)	Outlet Valve (OV)	Traction Control Valve (TCV)	High Pressure Switching Valve (HSV)	Return Pump
   Normal Braking	Close	Close	Closed (Partially)	Open	OFF

   
   

   

7. 7
   ESP Pressure Decrease Mode (controlled only for FR)

   	Inlet Valve (IV)	Outlet Valve (OV)	Traction Control Valve (TCV)	High Pressure Switching Valve (HSV)	Return Pump
   Normal Braking	Close	Open	Closed (Partially)	Open	ON (low engine speed control)

   
   

   

   

ESP Operation Mode. ABS Warning Lamp. The ABS warning lamp indicates the ABS self-check and malfunction status. The ABS warning lamp should illuminate:

• During the initialization phase after IGN ON (continuously for 3 seconds).
• In case of ABS operation failure during braking.
• In diagnostic mode.
• When the ECU connector is disconnected from the ECU.

EBD/Parking Brake Warning Lamp The EBD warning lamp indicates the EBD self-check and malfunction status. However, if the parking brake switch is ON, the EBD warning lamp always illuminates regardless of EBD function. The EBD warning lamp should illuminate:

• During the initialization phase after IGN ON (continuously for 3 seconds).
• When the parking brake switch is on or the brake fluid level is low.
• When the EBD function has failed.
• In diagnostic mode.
• When the ECU connector is disconnected from the ECU.

ESP Function/Warning Lamp (ESP System). The ESP function/warning lamp indicates the ESP self-check and malfunction status. The ESP function/warning lamp operates under the following conditions:

• During the initialization phase after IGN ON (continuously for 3 seconds).
• When ESP function is suppressed due to a failure.
• In diagnostic mode.
• When the ESP system is operating (flashing - 2 Hz).

ESP OFF Lamp The ESP OFF lamp indicates the self-diagnosis and operating status of the ESP. The ESP OFF lamp illuminates under the following conditions:

• During the initialization phase after IGN ON (continuously for 3 seconds).
• When the driver turns off the ESP function using the switch.

ESP On/Off Switch (ESP System). The ESP On/Off switch is used to switch the ESP function between on and off states at the driver's request. The On/Off switch must be a normally open, momentary contact switch. The initial state of the ESP function is on, and the switch is used to request a change of ESP state.