Subaru 1998 Forester Owner's Manual page 185

The ABS system prevents the lock-up of wheels which may occur during
sudden braking or braking on slippery road surfaces. This helps prevent
the loss of steering control and directional stability caused by wheel
lock-up.
When the ABS system is operating, you may hear a chattering noise or
feel a slight vibration in the brake pedal. This is normal when the ABS
operates.
B ABS system self-checking
You may feel a slight shock in the brake pedal and hear the operating
sound of ABS from the engine compartment just after the vehicle
started. These are caused by an automatic functional test of the ABS
system being carried out and does not indicate any abnormal condi-
tion.
B ABS warning light
The ABS warning light comes on when the ignition switch is turned to
the "ON" position and goes out after about two seconds.
This is an indication that the ABS system is working properly.
If the warning light behaves as follows, ABS system may not work
properly.
D The warning light does not come on when the ignition switch is
turned to the "ON" position.
D The warning light comes on when the ignition switch is turned to
the "ON" position, but it does not go out even when the vehicle speed
Starting and operating
HS0156
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