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



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 HBB connector B-107.
(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 (Refer to ). 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 HBB connector B-108.
(3)Measure the resistance between the terminals 33 and 35 at the HBB.
OK: Approx. 1 kΩ
(4)With the HBB connector B-108 disconnected, turn ON the ignition switch to operate the pump motor.
(5)During the pump motor operation, measure the resistance value (resistance value at high accumulator pressure) between the HBB-side connector terminal No. 33 and No. 35.
OK: 0 Ω

Q. Is the check result normal?
Go to Step 3.
Replace the master cylinder and hydraulic unit assembly (Refer to ). 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 (Refer to ).
(2)Disassemble the HBB (Refer to ).
(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 (Refer to ), install the HBB (Refer to ), refill the brake fluid, and bleed the brake line (Refer to ). Then go to Step 5.
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.

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 (Refer to ). Then go to Step 6.
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 .

STEP 6. Recheck for diagnosis code.
(1)Erase the diagnosis code.
(2)Recheck for diagnosis code.

Q. Is code No.78 set?
Replace the HBB (Refer to ). Then go to Step 7.
Go to Step 7.

STEP 7. Recheck for diagnosis code.
(1)Erase the diagnosis code.
(2)Recheck for diagnosis code.

Q. Is code No.78 set?
Start over at Step 1.
The procedure is complete.