Bosch 5.3 - ABS/EDL

ABS/EDL and ABS/EDL/ASR functions (Bosch 5-3)
The Bosch 5.3 ABS/EDL system has a compact design. The ABS return flow pump -V39-, the ABS hydraulic unit -N55- and the ABS control module -J104- are combined to form the hydraulic control unit.

CAUTION: The bolts that 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.
The two brake hydraulic circuits are split diagonally, one supplying left front and right rear brakes with the appropriate hydraulic pressure, the other supplying right front and left rear brakes.

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

Electronic Brake pressure Distribution (EBD)
Matched software stored in the ABS control module -J104-, performs the function of the conventional brake pressure regulator, the latter no longer being installed.

WARNING:
- If a malfunction has been detected by OBD, the ABS/EDL warning light and red brake warning symbol in the instrument cluster will light up.
- Bear in mind that the EBD function is not operating.
- The brake system functions are limited and there is a risk of accident. See "Road test".

EDL
The Electronic Differential Lock (EDL) is a traction control aid to driving away from a standstill. An electronically-controlled brake application at the wheel that is spinning provides a torque reaction point for the differential. This enables the wheel with better traction to make use of the engine power. EDL is effective in both forward and reverse. The EDL function operates up to a road speed of 40 km/h (25 mph).
All-wheel-drive models are equipped with EDL as standard equipment. The EDL control process on these vehicles can be activated at road speeds up to 40 km/h (25 mph), and it will remain active up to 80 km/h (50 mph) once it has been initiated.
Suction dampers are installed in the ABS hydraulic unit to improve the build-up of pressure in the relevant brake calipers when EDL is operating. EDL operating pressure is restricted to 170 ± 25 bar (2465 ± 363 psi) by a pressure limiting valve.
To eliminate the risk of the brakes overheating, EDL control cycles are no longer permitted once the brakes have reached a certain temperature limit, which is defined by ABS control module -J104-. Actual brake temperature is calculated by the control module using a computed model. EDL is operational again once the control module calculates a lower-limit brake temperature. Operation of the conventional braking systems, ABS, EBD and Anti-Slip Regulation (ASR) if so equipped, are not affected by this intervention in the system.
When the ignition is switched off, the calculated temperature of the hot brakes is stored in memory until the ignition is switched on again. When the ignition is switched on, the instrument cluster combination processor sends a time signal that enables the ABS control module -J104- to calculate the period the vehicle has been left standing. This period is put into the temperature simulation formula 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 broke temperature equal to the lowest value in the simulation formula.
If EDL is switched off because the temperature limit has been exceeded, this will be indicated in the measuring value block for a period of 20 ignition cycles, Refer to: Read Measuring Value Block. Read Measuring Valve Block

ASR
On vehicles equipped with ASR (traction control) it is important to check the control module coding. Programming and Relearning The ASR function requires an exchange of signals (a communication link) between the ABS control module -J104-, the Motronic Engine Control Module (ECM) and the Transmission Control Module (TCM).
ASR 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, ASR also incorporates an overrun torque limiting function (MSR). MSR prevents the drive to 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 idle air control.
ASR 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 affected by the ASR switch. 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 (3 times per sec.), Refer to: Read Measuring Value Block.