Bosch 5.3 ABS/EDL System, Function
The Bosch 5.3 system has a more 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. The bolts, which secure the individual components of the hydraulic control module, must not be unscrewed.
The direct connection between these components reduces possible sources of malfunctions. There is no provision for repairing the hydraulic control module - it must be replaced if necessary.
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 individual components of the Bosch 5.3 system have the functions:
Electronic brake force distribution
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 brake pressure limiter.
In the event of failure of the ABS, the signal which activates the ABS/EDL warning light and the brake system warning symbol is sent to the instrument cluster via the wire from contact 21 of ABS control module (w/EDL) -J104-. In vehicles built up to week 20/1997, the instrument cluster simply registers whether or not this signal is present: The brake system warning symbol normally comes on in addition to the ABS/EDL warning light.
In vehicles built from week 21/1997 onward, the brake system warning symbol no longer comes on at all times when a failure of the ABS has occurred.
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 has failed. In this condition the vehicle should only be driven with extra caution.
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. Refer to the notes in the table under "Check Control Module Version" for identification of what type of electronic brake force distribution function is installed in the vehicle.
ABS:
The Anti-Lock Brake System (ABS) prevents the wheels from locking when the brakes are applied by the driver.
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 transmit the engine power onto the road. The EDL is effective in both forward and reverse directions.
EDL is standard equipment on vehicles with all wheel drive, where it acts on all four wheels (on vehicles with front wheel drive it acts only on the front wheels). A mechanical differential lock is not required.
The EDL active control function can be initiated at road speeds up to 40 km/h. Once the EDL has become active, it cuts out automatically at a predetermined upper speed threshold, which is 40 km/h on vehicles with front wheel drive and 80 km/h on vehicles with all wheel drive.
Suction dampers are installed in the hydraulic unit to assist the build-up of pressure in the corresponding wheel brake cylinders when the EDL is active. The operating range of the pressure limiting valve in the hydraulic unit is 170 ± 25 bar.
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 by means of a simulation formula. The EDL is then reactivated when the calculated temperature drops below a predetermined lower threshold. The operation of the conventional brake system and the ABS function are not affected by this automatic cut-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 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 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 measured value block for a period of 20 ignition cycles.
ASR:
ASR (traction control system) is only installed on vehicles with front wheel drive. On these vehicles it is important to check the control module coding. The traction control function relies on an exchange of signals between ABS control module (w/EDL) -J104-, the engine control module and the transmission control module, in other words a communication link between the control modules.
There are two types of communication link in use:
^ Signals transmitted via a number of separate wires.
^ Signals transmitted via CAN-Bus. The CAN-Bus consists of only two wires, which transmit all the necessary signals.
You can establish which of these communication systems is employed, by using the function "Check Control Module Versions" and by referring to the table of control module versions.
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 act together to assist acceleration.
Depending on the engine version, the ASR also incorporates an overrun torque limiting 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 volume control.
If required, the ASR function can be switched off and then on again 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. The ASR will be activated again automatically the next time the ignition is switched on. When the system is deactivated, the ASR warning light comes on in the instrument cluster. The warning light flashes at a rate of three times per second when the control function starts working.