ABS/EDL (Bosch 5.3), Function

ABS/EDL (BOSCH 5.3), FUNCTION
The Bosch 5.3 ABS/EDL has a compact design. The ABS return flow pump -V39-, the ABS hydraulic unit -N55- and the ABS control module (W/EDL) -J104- are combined to form the hydraulic control module.

CAUTION: The bolts which secure the individual components of the hydraulic control unit must not be unscrewed

The direct connection between these components reduces possible sources of malfunctions. There is no provision for repairing the hydraulic control unit; it must be replaced if necessary.

Bosch 5.3 ABS/EDL Functions

ABS
The ABS prevents the wheels from locking when the brakes are applied by the driver.

EDL
The Electronic Differential Lock, may also be referred to as (EDS) is an aid used when driving away from a standstill. An electronically controlled brake application on the spinning driving 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. The EDL control process is available up to a road speed of 40 km/h (25mph).

All all wheel drive models are equipped with EDL. The EDL control process on these vehicles can be activated at road speeds up to 40 km/h (25mph), and it will remain active up to 80 km/h (50 mph) once it has been initiated.

ASR
On vehicles equipped with ASR (traction control system, also referred to as TCS) it is important to check the control module coding. The traction control function requires an exchange of signals (a communication link) between the ABS control module (W/EDL) -J104-, the Engine Control Module (ECM) and the Transmission Control Module (TCM).

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 EDL and ASR functions are combined in order to assist acceleration.

Depending on the Engine version, the ASR also incorporates an overrun torque limited function (MSR). MSR prevents the driven wheels from locking up due to excessive engine braking torque, for instance when the driver changes down from 3rd to 2nd gear. The engine braking effect is reduced via the idle air control.

The ASR function can be switched on and off by means of the ASR push-button switch in the center console. The MSR overrun torque limiting function is not effected by the ASR switch. The ASR will be activated again automatically when the ignition is switched on again. When the system is deactivated, the traction control indicator light lights up in the instrument cluster.

On vehicles with ABS/EDL and ABS/EDL/ASR, pressure dampers are installed in the hydraulic unit to improve the build-up of pressure in the relevant wheel cylinders when the EDL is operating. The operating pressure of the EDL is restricted to 170 +/- 25 bar (2465 +/- 363 psi) by a pressure limited valve.

The ABS and EDL on all-wheel drive models have the same function as with front-wheel drive. With all-wheel drive, the EDL controls all four wheels, not just the front wheels as on front-wheel drive models. This removes the need for a driver operated mechanical lock.

To prevent the brakes from overheating, the EDL control Function is suppressed if the temperature of the brakes exceeds a certain value which is defined in the ABS control module (W/EDL) -J104-. The temperature of the brakes is calculated by the control module using a simulation formula. The EDL is then reactivated if the calculated temperature drops below a predetermined lower threshold. The operation of the conventional brake system and the ABS and ASR traction control functions are not affected by this automatic shut-off feature.

When the ignition is switched off, the calculated temperature of the hot brakes is stored in the memory until the ignition is switched on again. When the ignition is switched on, the instrument cluster combination processor sends a time signal which enables the ABS control module (W/EDL) -J104- to calculate the period the vehicle has been left standing. This period is put into the temperature simulation formula to calculate to calculate the new temperature of the brakes. If the vehicle has been left standing for more than one hour, the control module will automatically assume a brake temperature equal to the lowest value in the simulation formula.

If the EDL is switched off because the temperature limit has been exceeded, this will be indicated in the measuring value block period of 20 ignition cycles.