HYDRAULIC BRAKE BOOSTER (HBB) HYDRAULIC UNIT CHECK


caution
  • The roller of the braking force tester and the tire should be dry during testing.
  • When testing the front brakes, apply the parking brake. When testing the rear brakes, stop the front wheels with chocks.
1.Jack up the vehicle. Then support the vehicle with rigid racks at the specified jack-up points or place the front or rear wheels on the rollers of the braking force tester.
2.Release the parking brake, and feel the drag force (drag torque) on each road wheel. When using the braking force tester, take a reading of the brake drag force.
caution To prevent damage to M.U.T.-III, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting M.U.T.-III.
3. Turn the ignition switch to the "LOCK" (OFF) position and set M.U.T.-III as shown in the illustration.
4.After checking that the selector lever is in neutral, start the engine.
5.Use M.U.T.-III to force-drive the actuator.
note
  • The ASTC system will switch to the scan tool mode and the ABS warning lamp will illuminate.
  • When the ASTC has been interrupted by the fail-safe function, M.U.T.-III actuator testing cannot be used.
6.

Turn the wheel by hand and check the change in braking force when the brake pedal is depressed. When using the braking force tester, depress the brake pedal until the braking force is at the following values, and check that the braking force changes to the brake drag force instep 2 when the actuator is force-driven. The result should be as shown in the diagram above.

    Front wheel: 785 - 981 N
    Rear wheel: 785 - 981 N
7.If the result of inspection is abnormal, repair according to the Diagnosis Table below.

Diagnosis Table
No.
Operation
Normal condition
Abnormal condition
Probable cause
Remedy
01

  1. Depress brake pedal to lock wheel.
  2. Using scan tool MB991958, select the wheel to be checked and force the actuator to operate.
  3. Turn the selected wheel manually to check the change of brake force.

Brake force releases for 3 seconds after locking.
Wheel does not lock when brake pedal is depressed.
Clogged brake line other than hydraulic brake booster (HBB)
Check and clean brake line
02
Clogged HBB
Replace HBB
03
Brake force is not released
Incorrect HBB brake tube connection
Connect correctly
04
HBB solenoid valve not functioning correctly
Replace HBB
8.After inspection, disconnect the M.U.T.-III immediately after turning the ignition switch to the "LOCK" (OFF) position.