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

Tech Tips

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

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

When either of the following is detected (after a condition is met, the code is stored and the buzzer sounds):


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

  2. The accumulator pressure has been low since system start and the pressure is less than 14.62 MPa for 120 seconds.

  • Brake accumulator pump

  • Skid control ECU
↑ 143

When any of the following is detected:


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

  2. The accumulator pressure decreases 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.

CAUTION / NOTICE / HINT

Note

When replacing the skid control ECU or brake actuator, perform initialization of linear solenoid valve and calibration Click here.

Tech Tips

When C1202/68, C1241/41, C1252/52, C1253/53 or C1391/69 are output together with C1256/57, inspect and repair the trouble areas indicated by C1202/68, C1241/41, C1252/52, C1253/53 or C1391/69 first.

PROCEDURE


  1. CONFIRM DTC


    1. Confirm output DTCs Click here.

      Result
      Result Proceed to
      DTC C1256 is output A
      DTC C1241, C1252, C1253, C1202 or C1391 is output B

    B

    CHECK CIRCUITS INDICATED BY OUTPUT DTC Click here

    A

  2. CUSTOMER PROBLEM ANALYSIS


    1. Perform customer problem analysis to confirm whether if the customer was frequently braking when the brake warning light/yellow (minor malfunction) was illuminated.

      Tech Tips

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

      Result
      Result Proceed to
      There was no frequent braking A
      There was frequent braking B

    B

    READ VALUE USING INTELLIGENT TESTER (ACCUMULATOR PRESSURE SENSOR) Click here

    A

  3. INSPECT BRAKE ACCUMULATOR PUMP


    1. Turn the engine switch off.

    2. A001BQ9E03
      *1 Component without harness connected: (Brake Accumulator Pump)
      *2 MTT

      Disconnect the A23 and A24 accumulator connectors.

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

      Standard resistance
      Tester Connection Condition Specified Condition
      A2 (BM1) - A4 (GND1) Always 10 Ω or less
      B2 (BM2) - A4 (GND1)
      A2 (BM1) - B2 (BM2) Always Below 1 Ω
      A4 (GND1) - B1 (GND2)
      A2 (BM1) - A1 (MTT) Always 950 to 1050 Ω
      B2 (BM2) - A1 (MTT)
      Result
      Result Proceed to
      OK A
      NG for LHD B
      for RHD C

    B

    REPLACE BRAKE ACCUMULATOR PUMP Click here

    C

    REPLACE BRAKE ACCUMULATOR PUMP Click here

    A

  4. READ VALUE USING INTELLIGENT TESTER (ACCUMULATOR PRESSURE SENSOR)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Select the Data List mode on the intelligent tester.

      Skid control ECU:
      Tester Display Measurement Item /Range Normal Condition Diagnostic Note
      Accumulator Sensor Accumulator pressure sensor / min.: 0.00 V, max.: 5.00 V Specified value: 2.60 to 3.80 V -

    4. Depress the brake pedal 4 or 5 times to operate the pump motor, and check the output value on the intelligent tester with the motor stopped (not braking) for 30 seconds.

      OK
      The accumulator pressure sensor voltage change is within 0.2 V.

    OK

    USE SIMULATION METHOD TO CHECK Click here

    NG

  5. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (SMC1, SMC2, SLRRR, AND SLRRL)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Select the ACTIVE TEST mode on the intelligent tester.

      Skid control ECU:
      Tester Display Test Part Control Range Diagnostic Note
      Electronically Controlled Brake System Solenoid (SCC) Turns electronically controlled brake system solenoid (SMC2) ON / OFF Operation sound of solenoid (clicking sound) can be heard
      Electronically Controlled Brake System Solenoid (SMC) Turns electronically controlled brake system solenoid (SMC1) ON / OFF Operation sound of solenoid (clicking sound) can be heard
      Electronically Controlled Brake System Solenoid (SLRRR) Valve Close Turns SLRRR solenoid ON / OFF Operation sound of solenoid (clicking sound) can be heard
      Electronically Controlled Brake System Solenoid (SLRRL) Valve Close Turns SLRRL solenoid ON / OFF Operation sound of solenoid (clicking sound) can be heard

    4. Using the intelligent tester, turn SMC1, SMC2, SLRRR, or SLRRL ON.

      A001FYQE01

    5. Check that each wheel cylinder's output value does not increase.

      OK
      Each wheel cylinder's output value does not increase.

      Tech Tips

      If any of wheel cylinder's output value increases, there may be a brake fluid leak in the brake actuator.

      Result
      Result Proceed to
      OK for LHD A
      for RHD B
      NG for LHD C
      for RHD D

    A

    REPLACE BRAKE ACCUMULATOR PUMP Click here

    B

    REPLACE BRAKE ACCUMULATOR PUMP Click here

    C

    REPLACE BRAKE ACTUATOR Click here

    D

    REPLACE BRAKE ACTUATOR Click here