Subaru Impreza 2002 Service Manual page 91

ABS
B: FUNCTIONS OF SENSORS AND ACTUATORS
Name
ABS control module and
hydraulic control unit
(ABSCM & H/U)
ABS sensors (wheel speed sensors)
Tone wheels
G sensor
Lateral G sensor (STi model)
Stop light switch
ABS warning light
Automatic transmission control module
Brake warning light
ANTI-LOCK BRAKE SYSTEM (ABS)
D It determines the conditions of the wheels and the vehicle body from the
ABSCM section
wheel speed data and controls the hydraulic unit depending on the re-
sult.
D When the ABS is active, the ABSCM provides the automatic transmis-
sion control module with control signals which are used by the module
for cooperative control of the vehicle with the ABSCM.
D Whenever the ignition switch is placed at ON, the module performs a
self diagnosis sequence. If anything wrong is detected, the module cuts
off the system.
D It communicates with the SUBARU select monitor.
D When the ABS is active, the H/U changes fluid passages to the wheel cylin-
H/U section
ders in response to commands from the ABSCM.
D It constitutes the brake fluid passage from the master cylinder to the wheel
cylinders together with the piping.
Valve relay section It serves as a power switch for the solenoid valves and motor relay coil. It
operates in response to a command from the ABSCM.
Motor relay section It serves as a power switch for the pump motor. It operates in response to
a command from the ABSCM.
They detect the wheel speed in terms of a change in the density of the
magnetic flux passing through them and convert it into an electrical signal.
The electrical signal is sent to the ABSCM.
They give a change in the magnetic flux density by the teeth around them-
selves to let the ABS sensors generate electrical signals.
It detects a change in acceleration in the longitudinal direction of the ve-
hicle and outputs it to the ABSCM as a voltage signal.
It detects lateral acceleration (G) during a turn and sends a voltage signal
proportional to the G value to the ABSCM.
It provides information on whether the brake pedal is depressed or not to
the ABSCM. The ABSCM uses it to determine ABS operation.
It alerts the driver to an ABS fault. When the diagnosis connector and diag-
nosis terminal are connected, the light flashes to indicate a trouble code
stored in the ABSCM.
It provides gear controls (fixing the speed at 3rd or changing power trans-
mission to front and rear wheels) in response to control signals from the
ABSCM.
It alerts the driver to an EBD fault. This warning light is also used for park-
ing brake warning and brake fluid level warning.
Function
ABS-4