Subaru Legacy/Outback

1999-2003 of release

Repair and operation of the car

System of anti-blocking of brakes (ABS) - the general information, the principle of functioning

Scheme of an arrangement of the ABS components and adjacent systems


1 — the Block the management/hydromodulator 2 — pressure Valve limiter 3 — the Diagnostic socket 4 — the Control lamp of ABS 5 — the DLC Socket for connection of SSM 6 — the Module of management of AT (TCM)	7 — Rotors of wheel sensors 8 — Wheel sensors 9 — Wheel cylinders 10 — the Sensor of overloads (G-sensor) 11 — the Sensor switch of stoplights 12 — GTTS

Functioning of the ABS hydromodulator in the mode of normal braking at passive ABS (on the example of a contour of one wheel)


1 — From GTTs 2 — the Damping chamber 3 — the Entrance port is open 4 — the Inlet electromagnetic valve 5 — the Control valve 6 — It is deactivated 7 — the Pump	8 — the Wheel cylinder 9 — the Final electromagnetic valve 10 — the Electric motor 11 — the Output port is closed 12 — It is deactivated 13 — the Tank

Functioning of the ABS hydromodulator in the pressure decrease mode (on the example of a contour of one wheel)


1 — From GTTs 2 — the Damping chamber 3 — the Entrance port is closed 4 — the Inlet electromagnetic valve 5 — the Control valve 6 — It is activated 7 — the Pump	8 — the Wheel cylinder 9 — the Final electromagnetic valve 10 — the Electric motor 11 — the Output port is open 12 — It is activated 13 — the Tank

Functioning of the ABS hydromodulator in the mode of deduction of pressure (on the example of a contour of one wheel)


1 — From GTTs 2 — the Damping chamber 3 — the Entrance port is closed 4 — the Inlet electromagnetic valve 5 — the Control valve 6 — It is activated 7 — the Pump	8 — the Wheel cylinder 9 — the Final electromagnetic valve 10 — the Electric motor 11 — the Output port is closed 12 — It is deactivated 13 — the Tank

Functioning of the ABS hydromodulator in the mode of increase of pressure (on the example of a contour of one wheel)


1 — From GTTs 2 — the Damping chamber 3 — the Entrance port is open 4 — the Inlet electromagnetic valve 5 — the Control valve 6 — It is deactivated 7 — the Pump	8 — the Wheel cylinder 9 — the Final electromagnetic valve 10 — the Electric motor 11 — the Output port is closed 12 — It is deactivated 13 — the Tank

Design and principle of functioning of the wheel sensor


1 — the sensor Case 2 — the Sensitive element 3 — the Rotor	4 — the Full speed of rotation 5 — the Lowered rotation speed 6 — the Permanent magnet

On the vehicles equipped with brake system of usual type, sharp squeezing of a pedal of a foot brake leads to blocking of wheels. Thus coupling of a protector with a paving is broken, and the car can start to skid, losing controllability. The system of anti-blocking of brakes (ABS) prevents premature blocking of wheels, continuously operating the speed of their rotation during braking due to modulations of pressure of hydraulic liquid in each of brake mechanisms.

ABS exit out of operation leads to activation of emergency operation at which normal functioning of usual brake system is provided, - on an instrument guard of the car the corresponding control lamp lights up.

The scheme of an arrangement of the ABS components and adjacent systems is submitted on an illustration.

Block management/hydromodulator

5.3i ABS in which the hydromodulator, the ABS control unit, the relay of valves and an electric motor for the purpose of simplification of service and weight reduction are united in the uniform assembly called by assembly of the module of the management/hydromodulator is included in the standard package of all Legacy/Outback models. The ABS control unit traces the speed of rotation of each of car wheels, being guided by the arriving signals from wheel sensors. When at emergency braking any of wheels it starts being blocked prematurely, the module of management gives out command for activation of the hydraulic modulator of the electromagnetic valve placed inside which, working, opens the corresponding site of a brake contour, letting out from it in the tank part of hydraulic liquid and, respectively, reducing working pressure.

In system like 5.3i pressure in each of forward wheels of the car is controlled and regulated individually, blocking of any of back wheels leads to uniform decrease in brake pressure in contours of both back brake mechanisms.

As soon as speeds of rotation of wheels are equalized, the valve is closed again, and pressure continues to rise. The cycle lasts fractions of a second on each of wheels and repeats until braking is not complete. The design of system allows to correct pressure in hydraulic contours of each of four wheels. Actually the scheme of functioning of ABS is much more difficult, than it can seem therefore authors of the present manual do not recommend to owners of cars to make attempt of independent performance of repair of system. In case of malfunctions it will be most reasonable to address to specialists of car service.

The valvate relay plays a role of the power switch of windings of electromagnetic valves and relay of an electric motor. Operation of the relay happens at the command of the control unit.

The relay of an electric motor provides management of functioning of the hydraulic pump.

Principle of functioning of the hydromodulator

The cycle of functioning of the hydromodulator consists of four operating modes: one passive, - the mode of normal braking (ABS is not activated), - and three active modes: mode of increase of pressure, mode of deduction of pressure and mode of pressure decrease.

The mode of normal braking (ABS is not activated)

In the mode of normal braking both (inlet and final) electromagnetic valves of the modulator are deactivated, i.e. the entrance port of the inlet valve is open, the output port of the final valve is closed and the pressure of hydraulic liquid developed in GTTs completely is transferred to the wheel cylinder.

The pressure decrease mode (ABS is activated)

Both (inlet and final) electromagnetic the valve are activated (the entrance port is closed, day off is open). In this state the wheel cylinder is isolated from GTTs, but connected to the tank and brake fluid can freely flow in the last that is followed by dumping of hydraulic pressure and decrease in brake effort.

The liquid accumulating in the tank is pumped over by the pump back in the main cylinder. On continuation of all cycle of this phase the pump continues to function.

The mode of deduction of pressure (ABS is activated)

The inlet electromagnetic valve is activated and its entrance port is closed. The final valve is deactivated, - its final port is also closed. All channels connecting the wheel cylinder to GTTs and the tank are blocked. As a result pressure keeps in the wheel cylinder.

On continuation of all cycle of this phase the pump continues to function.

The mode of increase of pressure (ABS is activated)

Both (inlet and final) electromagnetic the valve are deactivated (the entrance port of the inlet valve is open, the output port of the final valve is closed). In this state the working pressure forced by GTTs moves in the wheel cylinder promotes increase of brake effort.

On continuation of all cycle of this phase the pump continues to function.

Wheel sensors and their rotors

ABS exercises in the electric way control of pressure in brake mechanisms of all wheels of the car, preventing premature blocking of the last at sharp braking. Each of wheels is equipped with the individual sensor of turns. The sensor consists of a rotor (a ring with the teeth which are evenly located on its perimeter) and a sensitive element in the form of the podmagnichenny coil. The sensitive element of the sensor fixes the moments of passing of rotor teeths by it and will transform the received information to electric signals, the control of ABS which are continuously transferred on the module. By results of processing of the arriving signals the module of management receives information on the relative speed of rotation of each of wheels. While all four wheels rotate with an identical frequency, ABS stays in a passive state. As soon as any of wheels starts being blocked, the control unit fixes change of the entering signal and develops command for operation of the modulator which is instantly dumping pressure of hydraulic liquid in the brake mechanism of the corresponding wheel.

Sensor switch of stoplights

On the signals arriving from the sensor switch of stoplights, the control unit defines the moment when the driver squeezes out a pedal of a foot brake, at once activating ABS.

Sensor of overloads (G-sensor)

The G-sensor serves for identification of the longitudinal accelerations of the vehicle connected with acceleration / deseleratsiyey and issues on the ABS control unit information in the form of alarm tension.

Control lamp of ABS

The control lamp of ABS warns the driver about malfunctions of anti-blocking system. The electric chain of the control unit/hydromodulator is at the same time broken off and the brake system continues to work in the normal mode (as in the absence of ABS). At short circuit of plugs of the diagnostic socket the lamp can be used as the output equipment of the malfunction codes which are stored in memory of the processor.

Module of management of AT (TCM)

On the TCM models equipped with AT provides control of gear shifting and on the basis of arriving from the ABS control unit of information can make activation of the mode of restriction on the 3rd transfer (3D) or redistribution of power between lobbies and back wheels of the car.