ABS Anti-Lock Brakes (Mark IV)

WIRING DIAGRAM

ABS Anti-lock Brakes (Mark IV): Component Location:

COMPONENT LOCATION VIEW

ABS Anti-lock Brakes (Mark IV): Component ID:

COMPONENT ID
1 Battery in the engine bay.
22a Fuse board behind the access panel in the glove box.
29 Brake light switch beside the brake pedal.
47q ABS/ABS-TCS warning lamp in the main instrument display panel.
75 Distribution block, battery positive, on the battery tray.
159 Distribution terminal (+15 circuit), in main fuse box behind the glove box.
230 Distribution terminal (+30 circuit) in main fuse box behind the glove box.
291 A5S control module on the battery tray.
292 Main relay, ABS, in the main fuse box behind the battery.
293 Pump relay, ABS, in the main fuse box behind the battery.
296 ABS valve block on the hydraulic unit.
298FL Wheel sensor, left front, on left-hand steering swivel member.
298FR Wheel sensor, right front, on the right-hand steering swivel member.
298RL Wheel sensor, left rear, on the left-hand rear wheel hub.
298RR Wheel sensor, right rear, on the right-hand rear wheel hub.
302a Fuse board, ABS, in main fuse box behind the battery.
303a/ Diode, ABS, under the relay board in
303b the ABS main fuse box (302B).
445 (H16-1) Diagnostics test socket, below the steering wheel.
427 Motor, hydraulic pump (ABS/ABS- ASR MARK IV), on the hydraulic unit.
428 Pedal position sensor (ABS/ABS-ASR MARK IV) on the brake vacuum servo.
507 Control module, TCS V6, on a bracket under the left-hand seat.

2-Pin Connectors
H2-46 In the engine bay behind the bulkhead partition on the far left.
H2-47 In the engine bay behind the bulkhead partition on the far right.
H2-48 Under the rear seat on the left-hand side under the carpet.
H2-49 Under the rear seat on the right-hand side under the carpet.

10-Pin Connector
H10-17 On the valve block.

Grounding Points
G15 Grounding point, ABS, on the left-hand structural member, beside the ABS control module.
G16 Grounding point on the left-hand structural member.

DESCRIPTION OF OPERATION
The brake system in cars with Anti-lock Brakes (ABS) is electrically controlled and monitored. (ABS = Anti-lock Braking System).

The system consists of the following components:
^ A master cylinder with vacuum servo.
^ A hydraulic unit with
- inlet valves
- outlet valves
- hydraulic pump

The system operates in two different modes.

ABS mode: The hydraulic unit works only in the ABS mode and regulates the pressure to the inlet and outlet valves by means of the hydraulic pump.

The control module receives wheel speed data from a sensor on each wheel. If the wheels tend to lock, the control module regulates the braking power, i.e. the pressure in the brake lines, by means of electric control valves. Braking power is regulated individually on each wheel.

Normal mode: In normal mode, the system functions as a conventional braking system and servo power is achieved with the engine vacuum.

A warning lamp on the dashboard, the ABS system warning lamp (ANTI-LOCK), is connected to the brake system.

The ABS system components are supplied with current via fuses in main relay and fuse board 302 on the bulkhead partition in the engine bay.

Fuse 3 protects control module 291, fuse 2 valve block 296 via relay 292 and fuse 1 protects pump motor 427 via relay 293.

In addition, warning lamp 47q is supplied with current (+15 circuit) via fuse 13 when the ignition switch is in the Drive or Start position.

Power Supply
When the ignition switch is turned to the Drive position, pin 53 of the control module is supplied with current (+54 circuit). The control module then grounds main relay 292 via pin 34 and the relay operates. The unit is then supplied with current (+30 circuit) for actuation of the hydraulic unit's control valves.

Function Of The Warning Lamp When Starting
When the ignition key is turned to the Start position, the current (+54 circuit) supplied to main relay 292 is cut off and the relay releases. The warning lamp then lights up when it is grounded via diode 303a and the relay contacts.

When the ignition switch is subsequently turned to the Drive position, current (+54 circuit) is again supplied to main relay 292, which starts to operate. The control module now grounds the warning lamp via terminal 52. The lamp lights up briefly as a check.

Hydraulic Pressure
Every time the car is started, the hydraulic pump also starts so that the control module will be able to test the pump.

The hydraulic pump works only in the ABS mode.

Brake Lights Switch
During braking, the brake lights switch supplies the control module with data via pin 32. As a result, the system reacts more rapidly.

Control Module 291
Control module 291 is continuously supplied with wheel speed data from the four wheel speed sensors:
298FL front left
298FR front right
298RL rear left
298RR rear right

On the basis of wheel speed data from the sensors, the control module regulates braking power via the eight hydraulic valves 296 in the hydraulic unit.

Each wheel is regulated individually. Two valves, one inlet and one outlet, are provided for each function.

Left-hand Front Wheel
IFL inlet valve
OFL outlet valve

Right-hand Front Wheel
IFR inlet valve
OFR outlet valve

Left-hand Rear Wheel:
IRL inlet valve
ORL outlet valve

Right-hand Rear Wheel:
IRR inlet valve
ORR outlet valve

When no current is supplied, the inlet valves are open and the outlet valves are closed.

Pedal Position Sensor 428
Normally, when the car is braked, the system will be in the normal mode. However, if the control module receives information from any of the wheel sensors indicating that one of the wheels is starting to lock up, the system goes into ABS mode.

At the same moment as wheel lock-up starts, the pedal position sensor sends information to the control module on the position of the brake pedal.

If the brake pedal is depressed harder, the hydraulic pump starts and builds up pressure which forces the pedal back to its original position, i.e. the position it had when the wheels started to lock up.

When braking is normal again and wheel lock-up no longer occurs, the system leaves ABS mode and returns to normal mode.

This sequence can occur several times during the same application of the brakes.

ABS Warning Lamp 47q
The control module monitors the operation of the ABS system and in the event of a malfunction it lights ABS warning lamp 47Q (ANTI LOCK). When the lamp is on, the ABS function is inoperative and the brake system functions as a conventional system.

If one of the following faults occurs, the lamp lights up because the control module ceases to ground it via pin 34. Main relay 292 then releases and the lamp is grounded to grounding point G15 via the relay contact and diode 303a:
^ When the level of the signal from one of wheel sensors 298 is too low.
^ When there is a fault in main relay 292.
^ When there is a fault in the inlet and outlet valves in valve block 296.
^ When there is a fault in the hydraulic pump.
^ When there is an open circuit in the wiring harness (or in the connectors) connected to valve block 296, wheel sensors 298.
^ When there is a fault in the control module.

FAULT DIAGNOSIS
Faults detected by the electronic unit are stored in the memory as diagnostic trouble codes. Readouts of these can be obtained with an ISAT scan tool.