INSPECTION PROCEDURE 3: Diagnosis code No.53 (pump motor clogging), or
No.55 or No.57 is set, but no sound comes from HBB buzzer.
OPERATION
- The ASTC-ECU controls the buzzer by turning the power transistor in the
ASTC-ECU ON and OFF.
- The ASTC-ECU outputs the buzzer-sounding signal at the malfunction of the
hydraulic brake booster (HBB). (Also the ASTC-ECU turns on the brake warning
light at the same time.)
- The buzzer will sound under the following cases:
- When the pump motor is locked (Diagnosis code No.53 is
set).
- When the pump motor is energized abnormally for long period
(Diagnosis code No.55 is set).
- When the accumulator pressure is abnormally low (Diagnosis code
No.57 is set).
- When the solenoid valve temperature in the ASTC-ECU is
abnormally high (Diagnosis code is not set).
COMMENT ON TROUBLE SYMPTOM
The cause is probably an open circuit
at the buzzer circuit, a malfunction of the buzzer or a failure of buzzer
drive transistor in the ASTC-ECU.
PROBABLE CAUSES
- Damaged wiring harness or connector
- Malfunction of the buzzer
- Malfunction of the ASTC-ECU
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STEP 1. Check buzzer connector D-102 and ASTC-ECU connector D-232 for
loose, corroded or damaged terminals, or terminals pushed back in the
connector.
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Q.
Is the check result normal?
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 Go to Step 2.
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 Repair the faulty connector or
terminal. Then go to Step 8.
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STEP 2. Check the buzzer circuit at ASTC-ECU harness connector
D-232.
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(1)Disconnect ASTC-ECU connector D-232 and check at the
harness connector (component side).
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(2)Turn the ignition switch to the "ON" position.
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(3)Connect terminal 54 to body earth.
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Q.
Does the buzzer sound?
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Replace the ASTC-ECU (Refer to
GROUP 35C, ASTC-ECU  ). Then go to Step 8.
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Go to Step 3.
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STEP 3. Check the buzzer.
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(1)Remove the buzzer (Refer to ).
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(2)Connect the battery to the buzzer as shown
on the illustration.
Q.
Does the buzzer sound?
Go to Step 4.
Replace the buzzer
(Refer to ). Then go to Step 8
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STEP 4. Check the buzzer power supply circuit at buzzer harness
connector D-102.
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(1)Disconnect buzzer connector D-102, and measure at the
harness connector (component side).
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(2)Turn the ignition switch to the "ON" position.
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(3)Measure the voltage between terminal 1 and body
earth.
OK: Approx. 12 volts (battery positive
voltage)
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Q.
Is battery positive voltage (approx. 12 volts) present?
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Go to Step 5.
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Go to Step 6.
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STEP 5. Check the harness wires between buzzer connector D-102
(terminal 2) and ASTC-ECU connector D-232 (terminal 54).
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Q.
Is the check result normal?
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Go to Step 8.
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Repair or replace it. Then go to
Step 8.
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STEP 6. Check joint connector (6) D-113 <4M4>, joint
connector (5) D-111 <6G7>, intermediate connector D-230, joint
connector (4) D-34 and junction block connector D-405 for loose, corroded
or damaged terminals, or terminals pushed back in the
connector.
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Q.
Is the check result normal?
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Go to Step 7.
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Repair it. Then go to Step
8.
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STEP 7. Check the harness wires between buzzer connector D-102
(terminal 1) and junction block connector D-403 (terminal
2).
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Q.
Is the check result normal?
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Go to Step 8.
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Repair it. Then go to Step
8.
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STEP 8. Retest the system.
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(1)Apply a chock to the wheel.
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(3)When 120 seconds or more have been elapsed since the
engine was started, release the parking brake lever and fully depress the
brake pedal repeatedly 15 to 20 times within 10 seconds.
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Q.
Does the buzzer sound?
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The
procedure is complete.
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Start over at Step 1.
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