ABS Anti-Lock Brakes (Mark IV)
��(ABS Anti-lock Brakes (Mark IV):
WIRING DIAGRAM
Anti-lock Brakes (Mark IV): Component Location:
COMPONENT LOCATION VIEW
Anti-lock Brakes (Mark IV): Component ID:
COMPONENT ID
1 Battery in the engine bay.
22A Fuse board behind the cover flap 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 ABS control module on the battery tray.
292 Main relay, ABS, in main fuse box behind the battery.
293 Pump relay, ABS, in main fuse box behind the battery.
296 ABS valve block on the hydraulic unit.
298A Wheel sensor, front left-hand, on the left-hand steering swivel member.
298B Wheel sensor, front right-hand, on the right-hand steering swivel member.
298C Wheel sensor, rear left-hand, on the left-hand rear wheel hub.
298D Wheel sensor, rear right-hand, 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 the ABS main fuse box
303B (302B).
348 Scan tool diagnostics data link connector under the right-hand seat.
(H10-9)
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.
2-Pin Connectors
H2-46 In the engine bay behind the bulkhead on the far left.
H2-47 In the engine bay behind the bulkhead 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.
G15 Grounding point beside the ABS control module.
G16 Grounding point on the left-hand structural member.
G24 Grounding point, on the front righthand seat 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:
^ A master cylinder with vacuum servo.
^ A hydraulic unit with
- inlet valves
- outlet valves
- hydraulic pump.
The system works in two different modes.
ABS mode: The hydraulic unit only works in the ABS mode and regulates the pressure to the inlet and outlet valves with the help of the hydraulic pump.
The control module receives data on the wheel speed from a sensor on each wheel. If the wheels tend to lock, the control module regulates the power of the brakes, i.e. the pressure in the brake lines, with the help of electronic control valves. The braking force on the wheels is individually controlled.
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 is connected to the brake system, ABS system warning lamp (ANTI-LOOK).
The components in the ABS system receive voltage via fuses on relay and fuse board 302 in the engine bay on the bulkhead partition.
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 receives 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 brake system 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 in order for the control module to be able to test the pump.
The hydraulic pump only works in the ABS mode.
Brake Light Switch
During braking, the brake light switch supplies data to the control module via pin 32. As a result, the system reacts more rapidly.
Control Module 291
Control module 291 is continually supplied with data about the speed of the wheels from the four wheel speed sensors:
298A front left
298B front right
298C rear left
298D rear right
On the basis of data from the sensors on the speed of the wheels, the control module regulates the braking force via the eight hydraulic valves 296 in the hydraulic unit.
Control takes place individually on each wheel. 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 is in the normal mode. However, if the control module receives information from any of the wheel sensors suggesting that one of the wheels is starting to lock up, the system goes into ABS mode.
At the same moment as wheel lock-up begins, the pedal position sensor sends information to the control module on the position of the brake pedal.
If the brake pedal is depressed further, 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 wheel 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 braking period.
ABS Warning Lamp
The control module monitors the function of the ABS system and lights ABS warning lamp 47Q (ANTI LOCK) if any of the functions is faulty. 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
�4�(ABS Anti-lock Brakes (Mark IV): ISAT Scan Tool Readings:
Scan tool diagnostics using the ISAT scan tool.