Code No.57: Accumulator system (low pressure warning switch malfunction or
accumulator pressure too low)
OPERATION
The pressure switch (for low-pressure warning) monitors
brake fluid pressure inside of the hydraulic brake booster (HBB). When the
brake fluid pressure decreases abnormally, the pressure switch (for
low-pressure warning) is turned off and the brake fluid low-pressure warning
signal is output to the ASTC-ECU.
DIAGNOSIS CODE SET CONDITIONS
Diagnosis code No.57 is set if the
brake fluid pressure decreases, or the pressure switch (for low-pressure
warning) OFF seize-up occurs. In this case, the ASTC-ECU sounds the buzzer
continuously to inform the trouble of the driver and protects the pump motor
by activating the pump motor intermittently.
PROBABLE CAUSES
- Brake fluid leakage in the hydraulic brake booster (HBB)
- Malfunction of the accumulator [Integrated with the hydraulic brake
booster (HBB)]
- Malfunction of the pressure switch (for low-pressure warning)
[Integrated with the hydraulic brake booster (HBB)]
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STEP 1. M.U.T.-III diagnosis code.
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(1)Erase the diagnosis code.
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(2)Recheck for diagnosis code.
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 Carry out the troubleshooting for
code No.55 (Refer to  ). Then go to Step 6.
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 Go to Step 2.
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STEP 2. Check the pressure switch (for low-pressure warning) circuit
inside the HBB.
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(1)Depress the pedal repeatedly more than 40 times until the
pedal depressing force feels heavy with the ignition switch at the "LOCK"
(OFF) position to release the pressure of HBB power supply system.
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(2)Disconnect HBB connector B-107.
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(3)Measure the resistance between the terminals 1 and 5 at
the HBB.
OK: Approx. 5.7 kΩ
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(4)Turn ON the ignition switch to operate the pump motor, and
then check that the pump motor stops.
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(5)Measure the resistance value (resistance value at high
accumulator pressure) between the HBB-side terminal No. 1 and terminal No.
5.
OK: Approx. 1 kΩ
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Q.
Is the check result normal?
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Go to Step 3.
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Replace the master cylinder and
hydraulic unit assembly (Refer to ). Then go to Step 6.
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STEP 3. Check the leakage of brake fluid from the HBB
visually.
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Q.
Is there leakage of brake fluid from the HBB?
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Go to Step 4.
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Go to Step 5.
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STEP 4. Disassemble and check the HBB.
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(1)Remove the HBB (Refer to ).
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(2)Disassemble the HBB (Refer to ).
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(3)Check the HBB for the following points.
- Power piston assembly for rust, damage, wear and deterioration
- Master cylinder piston assembly for rust, damage, wear and
deterioration
- Inside of the hydraulic unit assembly cylinder for rust and
damage
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Q.
Are all of the checked items in good condition?
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Assemble the HBB (Refer to ), install the HBB (Refer to ), refill the brake fluid, and
bleed the brake line (Refer to ). Then go to Step 5.
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Replace the deficient parts,
assemble the HBB (Refer to ), install the HBB (Refer to ), refill the brake fluid, and
bleed the brake line (Refer to ). Then go to Step 6.
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STEP 5. Recheck for diagnosis code.
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(1)Erase the diagnosis code.
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(2)Recheck for diagnosis code.
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Replace the accumulator (Refer to
). Then go to Step 6.
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It can
be assumed that this malfunction is intermittent. Refer to GROUP 00, How to
Use Troubleshooting/Inspection Service Points - How to Cope
with Intermittent Malfunction .
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STEP 6. Recheck for diagnosis code.
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(1)Erase the diagnosis code.
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(2)Recheck for diagnosis code.
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Start over at Step 1.
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The
procedure is complete.
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