Subaru impreza 2002 Service Manual page 88

ABS
1. Anti-lock Brake System (ABS)
A: FEATURE
D
The 5.3i type ABS used in the Impreza has a hydraulic control unit, an ABS control module, a
valve relay and a motor relay integrated into a single unit (called "ABSCM & H/U") for circuit sim-
plicity and reduced weight.
D
The ABS electrically controls the brake fluid pressure to each wheel to prevent the wheel from
locking during braking on slippery road surfaces, thereby enabling the driver to maintain the
directional control.
D
If the ABS becomes inoperative, a fail-safe system is activated to ensure same level of braking
performance as with a conventional brake system. In that case, the warning light comes on to indi-
cate that the ABS is malfunctioning.
D
The ABS is a 4-sensor, 4-channel system; the front wheel system is an independent control de-
1
sign* , while the rear wheel system is a select-low control design*
*1: A system which controls the front wheel brakes individually.
*2: A system which applies the same fluid pressure to both the rear wheels if either wheel starts
to lock. The pressure is determined based on the lower of the frictional coefficients of both wheels.
D
The STi model is equipped with a Sports ABS. The Sports ABS is different from the standard ABS
with an electronic brake force distribution (EBD) function in that it has an additional lateral G sen-
sor. When the G sensor senses large lateral acceleration exceeding the predetermined level dur-
ing a turn, the ABS switches the rear braking control mode from the select-low control to the inde-
pendent control in order to improve the braking performance during cornering.
ANTI-LOCK BRAKE SYSTEM (ABS)
ABS-2
2
.