ESP, Function
ESP incorporates the functions of electronic brake force distribution, ABS, EDL and ASR. The individual elements of the system are as follows:
If required, the ASR and ESP control functions can be switched off and then on again by means of the ASR/ESP push-button switch in the center console. This switch is overridden when the driver presses the brake pedal: ESP will remain active at all times during braking. Both functions, ASR and ESP, will be reactivated automatically the next time the ignition is switched on.
The condition of the ASR/ESP switch can be verified using the function 08 "Read Measuring Value Block".
When the system is deactivated, the ASR/ESP warning light comes on in the instrument cluster. The warning light flashes at rate of three times per second when the control function starts working.
Electronic brake force distribution
The brake system is split diagonally into two hydraulic circuits: one supplying the front left and rear right brakes and one supplying the front right and rear left brakes.
The ABS control module (w/EDL) -J104- is programmed with specially designed software for electronic brake force distribution, which takes over the function of the mechanical or hydraulic brake pressure limiter.
In cases where a failure of the ABS has occurred, but the electronic brake force distribution function can still be maintained by a back-up feature, the signal sent to the instrument cluster is pulsed. The instrument cluster distinguishes between three conditions: no signal present, pulsed signal, and continuous signal present. The ABS/EDL warning light and the brake system warning symbol come on in accordance with the signal received.
1. Terminal 15
2. Signal for activation of ABS/EDL warning light and brake system warning symbol
3. Supply voltage for ABS/EDL warning light
4. Supply voltage for brake system warning symbol
A - During phase "A" (after ignition is switched on) the ABS/EDL warning light is activated for two seconds during the self-test by means of signal "2", and comes on. During this phase an internal function in the instrument cluster suppresses the activation of the brake system warning symbol.
B - During phase "B", signal "2" is not present. The ABS/EDL warning light and brake system warning symbol do not come on.
C - In phase "C", On Board Diagnostic (OBD) has detected a malfunction, which does not cause the electronic brake force distribution function to be switched off. Signal "2" is pulsed. Only the ABS/EDL warning light comes on.
D - In phase "D", On Board Diagnostic (OBD) has detected a malfunction, which causes the electronic brake force distribution function to be switched off. Signal "2" is present continuously. Both the ABS/EDL warning light and brake system warning symbol come on.
If the brake system warning symbol comes on, this indicates that the electronic brake force distribution function is out of action. If the vehicle has to be driven in this condition, extra caution is required.
For further information on the activation of the warning lights in connection with the electronic brake force distribution function refer to Table of warning light functions.
ABS:
The Anti-Lock Brake System (ABS) prevents the wheels from locking when the brakes are applied by the driver. It controls the brake pressure applied to the individual wheel brake cylinders according to the rates of acceleration and retardation at the wheels (which depend on the amount of wheel slip) in such a way that the wheels can develop maximum road adhesion and thus the best possible braking effect.
EDL:
The Electronic Differential Lock (EDL) is an aid when driving away from a standstill. An electronically controlled brake application on the spinning driven wheel provides a torque reaction point for the differential. This enables the wheel with better traction to make use of the engine power. The EDL is effective in both forward and reverse directions.
On vehicles with all wheel drive, EDL acts on all four wheels; a mechanical differential lock is not required.
In conjunction with ESP, the EDL is active at all speeds.
ASR:
The traction control function (ASR) requires an exchange of signals between ABS control module (w/EDL) -J104-, the engine control module and the transmission control module (automatics only), in other words a communication link between the control modules.
These signals are transmitted via CAN-Bus.
The ASR traction control system prevents the driven wheels from spinning under acceleration: the system operates by reducing engine torque and is active at all speeds. The SOL and ASR functions act together to assist acceleration.
ESP
The Electronic Stabilization Program (ESP) is designed to stabilize the dynamic handling response of the vehicle by counteracting any tendency toward oversteer or understeer. The familiar functions of electronic brake force distribution, ABS, EDL and ASR (traction control) are incorporated in the system, but the characteristic function of the ESP is a controlled brake application at individual wheels.
Examples:
In an oversteer condition the tail of the vehicle breaks out, and the vehicle rotates further about its vertical axis (rotational movement) than is required to maintain course through the corner. The system counteracts this excessive movement by applying a controlled braking force at the outside front wheel.
In an understeer condition the front end of the vehicle does not follow the required cornering radius, and breaks away toward the outside of the corner. The vehicle does not rotate far enough about its vertical axis to maintain course through the corner. The system increases the amount of rotation by applying a controlled braking force at the inside rear wheel.
With the exception of the new components described below, the locations of the system components are the same as with the Bosch 5.3 system.