TC/ABS

In the brake related part of the TCS system, the anti-lock brake system (Mark II) is the most important component. However, for the anti-spin function, an extra valve housing (TC block) has been added to the hydraulic unit. The system includes indicator and warning lamps.

The system receives data on the wheel speed via the wheel sensors. With the average speed of the rear wheels as a reference (used in the TCS mode), the control module can at any given moment control the degree of spin on one of the drive wheels (speed increase in relation to the rear wheels).

When wheelspin is about to happen and TCS control is about to take place, accumulator pressure is supplied through the TC block and the main valve to the front wheel circuits. Braking is then controlled using the inlet and outlet valves.

The components in the TC/ABS system are supplied with current via the fuses in relay and fuse board 302 in the engine bay on the bulkhead partition.
^ Fuse 1 (30A) protects pump motor 297 (via relay 293).
^ Fuse 2 (30A) protects control valves 295, 296 and 383 (via main relay 292).
^ Fuse 3 (10A) protects control module 382.
^ Warning lamps 47Q, 47Y and 47F as well as indicator lamp 47X receive 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, causing the relay to operate. The unit then receives current (+30 circuit) for operation of the hydraulic unit control valves.

Function Of Warning Lamps When Starting
Each time the car is started the brake system warning lamps light up to show the driver that they are intact and in working order. How the lamps light up in the event of a fault in the system is described in" Monitoring Functions "below.

When the ignition switch is turned to the Start position, current (+54 circuit) to main relay 292 is cut off, causing it to release. As a result, ABS warning lamp 470 is grounded to grounding point G15 via diode 303A and the relay contact. At the same time, warning lamp 47Y is grounded to grounding point G15 via diodes 303A and 385 and the relay contact.

Since the relay is always deactivated for at least 2 seconds when starting, the lamp will light up during this time. However, the lamp can light up for up to 60 seconds until the correct hydraulic pressure has been reached. When the ignition switch is turned to the Start position, the test mode will also be passed on the switch. Brake warning lamp 47F will then be grounded through ignition switch 20 which causes the lamp to light up.

Hydraulic Pressure
The pressure in the hydraulic unit's pressure accumulator is maintained at the correct level by means of a hydraulic pump driven by motor 297 and controlled by pressure and warning switch 294.

If the car is started when the pressure is below 140 bar, switch 4-1 will close. The coil in pump relay 293 is then grounded and motor 297 receives current via the relay contact.

When the hydraulic pump has pumped up the pressure in the pressure accumulator to 180 bar, the switch opens and the motor stops. When the pressure drops to 140 bar while the car is being driven, the switch closes again and the pump starts. The pump has to work for 10-15 seconds to raise the pressure from 140 to 180 bar.

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 382
Control module 382 continuously receives data about the wheel speed from the four wheel speed sensors:
298A front left
298B front right
298C rear left
298D rear right

On the basis of incoming speed data from the sensors, the control module then regulates the braking force on the wheels via the six hydraulic valves 296 in the hydraulic unit.

Braking force on the front wheels is regulated individually and on the rear wheels jointly. Two valves, one inlet and one outlet, are provided for each function.
Left-hand front wheel:
IFL intake valve
OFL outlet valve

Right-hand front wheel:
IFR intake valve
OFR outlet valve

Rear wheels (common circuit):
IR intake valve
OR outlet valve If no current is supplied, the in let valves are open and the outlet valves closed.

Valve Block 383
Valve block 383 contains two valves and a pressure sensor. The control module receives data from the pressure sensor when the brake is activated (contacts 2-3 open). The valves are supplied with battery positive voltage via pin 3 of the control module. To activate a valve, it is grounded via the control module.

Main valve 295 receives current and is open when the ABS system is in operation.

Pressure sensor in valve block 383
The control module receives data from the pressure sensor in the valve block about whether the brake is activated or not and whether the TC or ABS mode is in operation.

The signal from the pressure sensor is compared with the input signal from brake light switch 29.

TCS ON/OFF Switch 449
The TCS function can be turned off with switch 449. The speed of the car must be below 60 kmph. When the switch is depressed, test lamp 47Y lights up.

MONITORING FUNCTIONS
For the function of the lamps when starting, see above under" Function Of Warning Lamps When Starting".

Brake Fluid Level Warning Lamp
Brake warning lamp 47F lights up under the following circumstances:
^ if the level in the brake fluid reservoir drops to the MIN mark, the lamp is grounded to grounding point G2 via contact 4-3 in level sensor 299.
^ if the pressure in the hydraulic unit pressure accumulator drops below 105 bar, causing the lamp to be grounded to grounding point G2 via contact 2-1 in pressure and warning switch 294. The switch closes at 105 bar and opens at 134 bar. In this situation, the ABS warning lamp also lights up.

Both switches are normally open. The brake warning lamp is also fitted to cars without TC/ABS, but is then only used to warn the driver that the level of fluid in the brake fluid reservoir is getting low.

ABS And TCS CTRL Warning Lamp
The control module monitors the function of the TC/ ABS system. If one of the functions is faulty, warning lamp 47Q (ANTI LOOK) lights up for the ABS system and TCS CTRL 47Y for the TC system. When the lamps are on, the ABS and TC functions are inoperative and the brake system functions as a conventional brake system.

Since control module 382 grounds the lamps via pins 52 and 44, the lamps light up if the following faults develop:
^ if the level in the brake fluid reservoir drops below the MIN mark, contact 1-2 in level sensor 299 opens, breaking the connection between pins 51 and 8 of the control module. Contact 3-5 in pressure and warning switch 294 is normally closed. In this position, the brake warning lamp also lights up.
^ if the pressure in the hydraulic unit pressure accumulator drops below 105 bar, causing contact 3-5 in pressure and warning switch 294 to open. Contact 1-2 in level sensor 299 is closed if the level in the brake fluid reservoir is correct. The brake warning lamp also lights up.
^ when the level of the signal from one of wheel sensors 298 is too low.
^ The lamps also light up in the event of a grounding fault, pins 1 and 19.

In the case of the following faults, the lamps light up because the control module no longer grounds via pin 34. Main relay 292 therefore releases and the lamps are grounded to grounding point G15 via the relay contact and diodes 303A and 385:
^ open circuit in the wiring harness (or in the connectors) connected to valve block 296, wheel sensors 298 or main valve 295.
^ a fault in the control module.

In the case of the following faults, only the TCS CTRL lamp lights by pin 44 being grounded to the control module.
^ When there is a fault in the circuit to the brake light switch.
^ When there is a fault in the circuit to the pressure switch in valve block 383. In the case of these faults, the TC has no effect on the brakes.
^ If there is an open circuit, short circuit or incorrect level, pin 4 or 24. The TO system will not operate the throttle butterfly.
^ If the front brake pads are overheated (temperature over 400°C).

IMPORTANT: This fault will cause the lamp to flash. When the pads have cooled down (300°C), the lamp goes out.

TCS Indicator Lamp
When the TC system is in operation, indicator lamp 47X lights by pin 7 being grounded to control module 382