Power Supply, Hydraulic Pressure and Monitoring Functions
ABS Diagrams:
ABS Components:
Locations of components
1 Battery
On the right-hand side of the engine compartment
2 Alternator
On the left-hand side of the engine
7 Earthing point
On the radiator cross-member
20 Ignition switch
On the centre console between the front seats
21 Ignition switch relay
In the electrical distribution box, in the engine compartment, relay position E
22A Fuse holder
In the electrical distribution box, in the engine compartment, on the left-hand wheel housing
47E Charging warning lamp
47F Brake warning lamp
47K SHIFT UP warning lamp
In the combined instrument in the instrument panel
47Q ABS warning lamp
In the combined instrument on the fascia
47T SRS Airbag warning lamp
In the combined instrument on the fascia
57 3-pole connector
One at the right-hand front wheel sensor
One at the left-hand front wheel sensor
58 12-pole connector
On the inside of the knee shield, to the left of the steering column
59 2-pole connector
At the electrical distribution box at the left-hand wheel housing on the left-hand side, under the back seat (1990 model) in the electrical distribution box in the engine compartment (CAB)
One in the engine compartment, at the hydraulic unit
One in the engine compartment, on the right-hand side of the bulkhead partition one under the back seat, on the left-hand side
One under the back seat, on the right-hand side
60 Single-pole connector
In the electrical distribution box, on the left-hand wheel housing (1990 model)
65 Earthing point
At the back seat (1990 model)
75 Distribution block
In the engine compartment, on the right-hand side
93 Earthing point
On the left-hand wheel housing member
98 10-pole connector
One (black) on the inside of the knee shield, to the left of the steering column
One at the electronic unit
123 4-pole connector
Two at the electronic unit. One black (left-hand front sensor) and one grey (right-hand front sensor)
152A 29-pole white connector
In the engine compartment, in the electrical distribution box on the left-hand wheel housing. The connector is accessible from the interior of the car.
152B 29-pole red connector
In the electrical distribution box in the engine compartment, on the left-hand wheel housing. The connector is accessible from the interior of the car.
152C 29-pole black connector
In the electrical distribution box in the engine compartment, on the left-hand wheel housing. The connector is accessible from the interior of the car.
158 Negative distribution terminal
In the electrical distribution box in the engine compartment, on the left-hand wheel housing
211 Earthing point
On the gearbox
257 Earthing point
On the alternator bracket
291 ABS control unit
On the left-hand side of the engine compartment, forward of the wheel housing (1989 model) under the back seat, on the right-hand side (1990 model)
292 ABS system relay
In the engine compartment, forward of the left-hand wheel housing, in the ABS electrical distribution box (1989 model)
In the engine compartment, behind the right-hand wheel housing, in the ABS electrical distribution box (1990 model)
293 ABS pump relay
In the engine compartment, forward of the left-hand wheel housing, in the ABS electrical distribution box (1989 model)
In the engine compartment, behind the right-hand wheel housing, in the ABS electrical distribution box (1990 model)
294 ABS pressure switch
In the engine compartment, on the hydraulic unit
295 ABS master valve
In the engine compartment, on the hydraulic unit
296 ABS valve block
In the engine compartment, forward of the left-hand wheel housing
297 ABS hydraulic pump motor
In the engine compartment, on the hydraulic unit
298A Wheel sensor, left-hand front
On the left-hand steering swivel member
298B Wheel sensor, right-hand front
On the right-hand steering swivel member
298C Wheel sensor, left-hand rear
On the left-hand rear wheel hub
298D Wheel sensor, right-hand rear
On the right-hand rear wheel hub
299 ABS brake fluid level sensor
In the engine compartment, on the brake fluid reservoir of the hydraulic unit
300 Earthing point on the hydraulic unit
In the engine compartment, on the front of the hydraulic unit
302 ABS electrical distribution box
In the engine compartment, forward of the left-hand wheel housing (1989 model) in the engine compartment, behind the right-hand wheel housing (1990 model)
302A ABS fuse holder
In the engine compartment, forward of the left-hand wheel housing, in the ABS electrical distribution box (1989 model)
In the engine compartment, behind the right-hand wheel housing, in the ABS electrical distribution box (1990 model)
303A ABS diode
303B ABS diode
In the engine compartment, forward of the left-hand wheel housing, in the ABS electrical distribution box (1989 model)
In the engine compartment, behind the right-hand wheel housing, in the ABS electrical distribution box (1990 model)
330 10-pole airbag test connector
In the centre console, under the rubber bellows, forward of the gear lever
331 Electronic unit for the airbag
In the fascia, under the left-hand speaker grille
332A Sensor, left-hand
In the engine compartment, forward of the left-hand wheel housing
332B Sensor, right-hand
In the engine compartment, forward of the right-hand wheel housing
333 Airbag
In the steering wheel
334 Earthing point for the electronic unit and test connector
Adjacent to the electronic unit
335 2-pole orange connector
The pins are short-circuited when the connector is separated
336 Slip-ring contact
In the steering wheel
397 Diagnostic test socket, ABS
In the engine compartment, in the cable harness at the hydraulic unit (1990 model)
400 Redundant earth for the airbag
On the left-hand wheel housing, accessible from the interior
Operation
Brake warning lamp
Brake warning lamp 47F will light up under the following circumstances:
- if the level in the fluid reservoir reaches the MIN mark on the reservoir. The lamp will then be earthed at earthing point 300 across contacts 4 - 3 of level sensor 299.
- if the pressure in the accumulator of the hydraulic unit should drop below 105 bar. The lamp will then be earthed at earthing point 7 across contacts 2 - 1 of pressure switch 294. The contacts close at 105 bar and open at 134 bar. (In this case, the ABS warning lamp will also light up.)
Both pairs of contacts are open under normal operating conditions.
Cars without ABS are also equipped with the brake warning lamp, although it is then used only for warning the driver that the level in the brake fluid reservoir is too low.
ABS warning lamp
The control unit monitors the performance of the ABS system and, if a fault should occur, will light up ANTI LOCK warning lamp 47Q. When the lamp is alight, the ABS function is inoperative, and the brake system wilt perform as a conventional brake system.
The following faults will cause pin 27 of control unit 291 to earth the lamp, thus lighting it up:
- if the level in the brake fluid reservoir should drop below the MIN marking on the reservoir. Contacts 1 - 2 of level sensor 299 will then open, thus opening the circuit between pins 9 and 10 of the control unit. Under normal operating conditions, contacts 3 - 5 of pressure switch 294 are closed. (In this case, the brake warning lamp will also light up.)
- if the pressure in the accumulator of the hydraulic unit should drop below 105 bar. Contacts 3 - 5 of pressure switch 294 will then open. Contacts 1 - 2 of level sensor 299 are closed if the level in the brake fluid reservoir is correct. (The brake warning lamp will also light up.)
- if the signal level from one of the wheel sensors 298 is too low.
The following faults will cause pin 8 of the control unit to be de-energized. ABS system relay 292 will then trip and the lamp will be earthed at earthing point 300 across the relay contacts and diode 303A.
- open-circuit in the wiring (or in the connector) to valve block 296, wheel sensors 298 or master valve 295.
- fault in the control unit.
Summary of indications provided by the warning lamps:
Brake fluid warning lamp lights up
Only the brake fluid level warning lamp will light up if the brake fluid level has dropped slightly.
Normal braking and ABS control remain unaffected.
ABS warning lamp lights up
Only the ABS warning lamp will light up if the electronic control unit should detect a fault in the ABS system.
The ordinary brakes operate normally but the ABS system is disconnected.
Brake fluid level warning and ABS warning lamps light up simultaneously
If both lamps are alight, this indicates either that the brake fluid in the reservoir has dropped further or that the hydraulic pressure has dropped to below 105 bar (1523 psi). This means that ABS control is inoperative and only reduced braking effort is available.
Joint activation due to low brake fluid level indicates that brake fluid is leaking out of the brake system.
Stop Immediately and don't drive the car until repairs have been carried out.
Joint activation due to low hydraulic pressure indicates that the servo action and the brake pressure at the rear wheels are not proportional to the pedal pressure. Finally, when the hydraulic pressure is 0 bar, there will be no servo action and no brake pressure to the rear wheels. The front-wheel brakes will operate normally, although without power assistance.