ABS
ANTI-LOCK BRAKE SYSTEM (ABS)
ABS-3
B: FUNCTIONS OF SENSORS AND ACTUATORS
Name Function
ABS control module and
hydraulic control unit
(ABSCM & H/U)
ABSCM section
! It determines the conditions of the wheels and the vehicle body from the
wheel speed data and controls the hydraulic unit depending on the result.
! When the ABS is active, the ABSCM provides the automatic transmission
control module with control signals which are used by the module for co-
operative control of the vehicle with the ABSCM.
! 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.
! It communicates with the SUBARU select monitor.
H/U section
! When the ABS is active, the H/U changes fluid passages to the wheel cyl-
inders in response to commands from the ABSCM.
! 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.
ABS sensors (wheel speed sensors) They detect the wheel speed in terms of a change in the density of the mag-
netic flux passing through them and convert it into an electrical signal. The
electrical signal is sent to the ABSCM.
Tone wheels They give a change in the magnetic flux density by the teeth around them-
selves to let the ABS sensors generate electrical signals.
G sensor It detects a change in acceleration in the longitudinal direction of the vehicle
and outputs it to the ABSCM as a voltage signal.
Stop light switch It provides information on whether the brake pedal is depressed or not to the
ABSCM. The ABSCM uses it to determine ABS operation.
ABS warning light 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.
Automatic transmission control module 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.
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