Electro-Hydraulic Control Unit; Electronic Control Unit - Fiat 1998 Marea Service Manual

Braking system
Anti-lock brakes
33.
The system is completed by:
- the hydraulic system pipes;
- specific electric wiring;
- a switch on the brake pedal for detecting the braking condition;
- an ABS warning light and a braking system failure warning light, in the instrument panel.

ELECTRO-HYDRAULIC CONTROL UNIT

The electro-hydraulic control unit is composed of two sections fixed to one another: an electronic con-
trol unit and an electro-hydraulic control unit.
The electronic control unit is connected to the A.B.S. wiring by means of a multiple connector.
On the basis of the signals coming from the sensors and with the aid of programmes stored in its memo-
ries, the electronic control uni.t operates the electro-hydraulic control unit.
The electro-hydraulic control unit is connected to the brake pump and the A.B.S. components through
the braking system pipes.

Electronic control unit

The electronic control unit is made up of hybrid circuits with resistances, diodes, transistors and inte-
grated logic circuits. The core of the system comprises two CMOS microprocessors with 24 K of ROM.
The main 16 bit processor calculates the ABS responses and constantly controls the operation of the
system, ensuring the safety (fail-safe), whilst the 8 bit (secondary) processor independently checks the
wheel speed signals; when the results obtained correspond, the electronic control unit issues the oper-
ating command to the electro-hydraulic control unit.
If this is not the case, if, for example, there is a fault in the anti-lock braking system, the device excludes
itself and braking takes place conventionally; at the same time, the failure warning light in the instrument
panel comes on.
The information relating to the fault is recorded in a non volatile memory; in effect, one of the two micropro-
cessors has a CMOS EEPROM memory whose contents are presevered even if the battery voltage is cut off.
This memory also has the task of preserving the fault codes to be read later using the diagnostic equipment.
1. Electronic control unit
2. Electro-hydraulic control unit
2
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