ELECTRONICALLY CONTROLLED BRAKE SYSTEM, Diagnostic DTC:C1256/57

DTC Code DTC Name
C1256/57 Accumulator Low Pressure

DESCRIPTION

The accumulator pressure sensor is built into the actuator and detects the accumulator pressure.

The skid control ECU assembly turns on the brake warning light / yellow (minor malfunction) and sounds the skid control buzzer if it senses a decrease in the accumulator pressure.

DTC C1256/57 may be output if the accumulator pressure drops due to frequent braking (this is not a malfunction).

DTC Code INF Code DTC Detection Condition Trouble Area
C1256/57 141

Either of the following is detected:


  1. When inputting the vehicle speed, the brake operation is input with the accumulator pressure low or the accumulator pressure extremely decreased while braking for 0.3 seconds or more.

  2. The accumulator pressure has been low since system start and pressure is less than 14.62 MPa for 0.8 seconds (stores the DTC after the conditions are met, and sounds buzzer).

  • Accumulator pressure dropped due to frequent brake pedal operation (not a malfunction)

  • Pump motor malfunction

  • Accumulator deterioration

  • Brake fluid leak

  • Accumulator pressure sensor (Brake booster with master cylinder assembly)

  • Supply voltage reduced
↑ 143

Any of the following is detected:


  1. When inputting the vehicle speed, any of the wheel cylinder pressure sensor values is less than the specified value with the accumulator pressure low for 0.5 seconds or more.

  2. The accumulator pressure decreased without increasing the wheel cylinder pressure of each wheel.

  3. With the motor relay abnormal or off, the accumulator pressure is less than 14.62 MPa for 0.5 seconds or more.

 ↑

WIRING DIAGRAM

Refer to DTCs C1252/52 and C1253/53 Click here.

INSPECTION PROCEDURE

Note

When replacing the brake actuator assembly, perform initialization and calibration of the linear solenoid valve Click here.

Tech Tips

When C1241/41, C1252/52 and/or C1253/53 are output together with C1256/57, inspect and repair the trouble areas indicated by C1241/41, C1252/52, C1253/53 and/or C1391/69 first Click here, Click here or Click here.

PROCEDURE


  1. BRAKE PROBLEM CHECK


    1. Ask the customer if frequent braking was performed while the brake warning light / yellow (minor malfunction) was on.

      OK
      Result Proceed to
      Frequent braking was not performed A
      Frequent braking was performed B

      Tech Tips

      This DTC is output even if the accumulator pressure drops only temporarily due to frequent braking.


    B

    END

    A

  2. INSPECT BRAKE ACTUATOR ASSEMBLY


    1. A01FTLYE17
      Text in Illustration
      *A for LHD
      *B for RHD
      *a

      Component without harness connected

      (Brake Actuator Assembly)

      Turn the power switch off.

    2. Make sure that there is no looseness at the locking part and the connecting part of the connectors.

    3. Disconnect the A12 brake actuator assembly connector.

    4. Measure the resistance according to the value(s) in the table below.

      Standard Resistance
      for LHD
      Tester Connection Condition Specified Condition
      2 (BM1) - 31 (GND1) Always Below 1 Ω
      2 (BM1) - 32 (GND2) Always Below 1 Ω
      1 (BM2) - 31 (GND1) Always Below 1 Ω
      1 (BM2) - 32 (GND2) Always Below 1 Ω
      2 (BM1) - 33 (MTT) Always 450 to 550 Ω
      1 (BM2) - 33 (MTT) Always 450 to 550 Ω
      for RHD
      Tester Connection Condition Specified Condition
      31 (BM1) - 1 (GND1) Always Below 1 Ω
      31 (BM1) - 2 (GND2) Always Below 1 Ω
      32 (BM2) - 1 (GND1) Always Below 1 Ω
      32 (BM2) - 2 (GND2) Always Below 1 Ω
      31 (BM1) - 3 (MTT) Always 450 to 550 Ω
      32 (BM2) - 3 (MTT) Always 450 to 550 Ω

    NG

    REPLACE BRAKE ACTUATOR ASSEMBLY Click here

    OK

  3. READ VALUE USING GTS (ACCUMULATOR PRESSURE SENSOR)


    1. Reconnect the brake actuator assembly connector.

    2. Connect the GTS to the DLC3.

    3. Turn the power switch on (IG).

    4. Select the Data List on the GTS Click here.

      ABS/VSC/TRC
      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Accumulator Sensor

      Accumulator pressure sensor /

      Min.: 0.00 V, Max.: 5.00 V

      		 Specified value: 2.6 to 3.8 V When brake fluid is stored in the accumulator: Accumulator pressure changes in accordance with volume of fluid stored in the accumulator

    5. Depress the brake pedal 4 or 5 times to operate the pump motor.

    6. Wait for 30 seconds without depressing the brake pedal.

    7. Check that the accumulator pressure sensor output value change is within the specified range.

      OK
      Accumulator pressure sensor output value change is less than 0.2 V.

    NG

    REPLACE BRAKE ACTUATOR ASSEMBLY Click here

    OK

    CHECK FOR INTERMITTENT PROBLEMS Click here