Section III Brake System
The brake system is used to transform the force on the brake pedal from the driver to braking force
of all wheels. Then the hydraulic system will distribute the braking force to each wheel. The
vacuum brake booster is used to decrease the force from the pedal and increase the hydraulic
pressure. The parking brake operates by rear wheels and controls the operation manually.
LF620 sedan has two brake systems, namely driving brake system and parking brake system. The
driving brake system is an engine vacuum booster ABS hydraulic brake system. And the parking
brake is to control the rear brake by cable system which utilizes the self-adjusting ratchet and pawl
structure. The ABS is controlled by the hydraulic control unit (HCU) in the hydraulic system, and
only works when the vehicle speed sensor detects that the wheels are locked.
I. Fault Diagnosis
The fault elimination of brake system is shown in Table 2-4. The figures in the Table refer to the
sequence of possible faults. Check all components and parts in sequence. Replace related parts if
necessary.
Table 2-4
Fault Possible Cause Actions
Alignment angle of wheels Check the alignment angle of wheels.
Brake pad Check and install a new component if necessary.
Brake disc Check and install a new component if necessary.
Brake runs off or drifts
Brake caliper Check and install a new component if necessary.
Brake fluid level sensor Refer to WDS.
Parking brake control device Release and adjust the parking brake.
Excessively worn brake pad Check and install a new component if necessary.
Red brake warning lamp is
lighted continuously
Main piston rod of braking master
pump
Install a new braking master pump.
Brake pad Check and install a new component if necessary.
Brake caliper Check and install a new component if necessary.
Vibration during brake action
Brake disc Check and install a new component if necessary.
With air in system Discharge the air in system.
Braking master pump Check the braking master pump.
Brake disc Check and install a new component if necessary.
Rapidly sunken
pedal
Brake pad Check and install a new component if necessary.
Brake caliper Check and install a new component if necessary.
Slowly sunken pedal
Brake master pump Check the brake master pump.
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