Code No.78: Accumulator
system (Motor energized too long 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 sent to the ABS-ECU.
DIAGNOSIS CODE SET CONDITIONS
The diagnosis code is set if the brake warning lamp illuminates along with the HBB buzzer
sound because the pressure switch (for low pressure warning) is operated by the decreased brake
fluid pressure.
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)]
Malfunction of the HBB pump [Integrated with the hydraulic brake booster
(HBB)]
DIAGNOSIS
STEP 1. Check the pressure switch (for low-pressure warning)
circuit inside the HBB.
(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.
(2)Disconnect B-107 HBB connector.
(3)Measure the resistance between the terminals 1 and 5 at the HBB. OK: Approx. 5.7 kΩ
(4)Turn ON the ignition switch to operate the pump motor, and then check that the
pump motor stops.
(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
Q.
Is the check result normal?
Go to Step 2.
Replace the master cylinder and hydraulic unit assembly. Then go to Step 7.
STEP 2. Check the pressure switch (for pump motor control) circuit
inside the HBB.
(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.
(2)Disconnect B-108 HBB connector.
(3)Measure the resistance between the terminals 33 and 35 at the HBB. OK: Approx. 1 kΩ
(4)Connect HBB connector B-108 to the vehicle wiring harness, and then turn the ignition
switch ON. The pump motor should run and then stop. Turn the ignition switch to the LOCK (OFF)
position to disconnect HBB connector B-108. At the HBB side, measure the resistance value (at
high accumulator pressure) between Nos. 33 and 35 terminals. OK: Continuity exists (2 Ω or less)
Q.
Is the check result normal?
Go to Step 3.
Replace the master cylinder and hydraulic unit assembly. Then go to Step 6.
STEP 3. Check the leakage of brake fluid from the HBB visually.
Q.
Is there leakage of brake fluid from the HBB?
Go to Step 4.
Go to Step 5.
STEP 4. Disassemble and check the HBB.
(1)Remove the HBB.
(2)Disassemble the HBB.
(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
Q.
Are all of the checked items in good condition?
Assemble the HBB, install the HBB, refill the brake fluid, and bleed the brake
line. Then go to Step 5.
Replace the deficient parts, assemble the HBB, install the HBB, refill the brake
fluid, and bleed the brake line . Then go to Step 6.
STEP 5. Recheck for diagnosis code.
(1)Erase the diagnosis code.
(2)Recheck for diagnosis code.
Q.
Is code No.78 set?
Replace the accumulator. Then go to Step 6.
It can be assumed that this malfunction is intermittent.
)
)
)
Go to Step 2.
Replace the master cylinder and hydraulic unit assembly. Then go to Step 7.