Code No.56: Pressure switch system <open circuit or short circuit (low pressure warning)>












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 ASTC-ECU.
  • The pressure switch (for pump motor control) monitors brake fluid pressure inside of the hydraulic brake booster (HBB). When the brake fluid pressure decreases lower than the specified value, the pressure switch (for pump motor control) is turned off and outputs the pump motor drive signal to the ASTC-ECU.
  • The ASTC-ECU monitors an open circuit of the pressure switch (for pump motor control) (at 11 terminal).
  • The ASTC-ECU monitors an open circuit or short circuit of the pressure switch (for low-pressure warning) (at 57 terminal).

DIAGNOSIS CODE SET CONDITIONS



note
  • Diagnosis code No.55 will be set if the pressure switch (for pump motor control) is stuck on.
  • Diagnosis code No.57 will be set if the pressure switch (for low-pressure warning) is stuck off.

PROBABLE CAUSES



  • Malfunction of the master cylinder and hydraulic unit assembly [Integrated with the hydraulic brake booster (HBB)]
  • Damaged wiring harness or connector
  • Malfunction of the ASTC-ECU

DIAGNOSIS

STEP 1. Check HBB connector B-107 and B-108 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is the check result normal?
Go to Step 2.
Repair the faulty connector or terminal. Then go to Step 8.

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 8.

STEP 3. 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 4.
Replace the master cylinder and hydraulic unit assembly (Refer to ). Then go to Step 8.

STEP 4. Check the following harness wires.

  • The wire between HBB connector B-107 (terminal 1) and body earth
  • The wire between HBB connector B-108 (terminal 33) and body earth

Q. Is the check result normal?
Go to Step 5.
Repair or replace it. Then go to Step 8.

STEP 5. Check ASTC-ECU connector D-233 and D-232 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q. Is the check result normal?
Go to Step 6.
Repair the faulty connector or terminal. Then go to Step 8.

STEP 6. Check the following harness wires.

  • The wire between HBB connector B-107 (terminal 5) and ASTC-ECU connector D-232 (terminal 57)
  • The wire between HBB connector B-108 (terminal 35) and ASTC-ECU connector D-233 (terminal 11)

Q. Is the check result normal?
Go to Step 7.
Repair or replace it. Then go to Step 8.

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

Q. Is code No.56 set?
Replace the ASTC-ECU (Refer to GROUP 35C, ASTC-ECU ). Then go to Step 8.
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 8. Recheck for diagnosis code.
(1)Erase the diagnosis code.
(2)Recheck for diagnosis code.

Q. Is code No.56 set?
Start over at Step 1.
The procedure is complete.