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.

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 120 seconds (stores the DTC after the conditions are met, and sounds buzzer).

  • Accumulator pressure

  • Brake actuator assembly (Accumulator pressure sensor)

  • Brake booster pump
↑ 143

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 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 BOOSTER PUMP


    1. A01NECCE09
      Text in Illustration
      *1

      Component without harness connected

      (Brake Booster Pump)

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

    2. Disconnect the brake booster pump connectors.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A83-2 (BM1) - A83-4 (GND1) Always Below 10 Ω
      A84-2 (BM2) - A83-4 (GND1) Always Below 10 Ω
      A83-2 (BM1) - A84-2 (BM2) Always Below 1 Ω
      A83-4 (GND1) - A84-1 (GND2) Always Below 1 Ω
      A83-2 (BM1) - A83-1 (MTT) Always 950 to 1050 Ω
      A84-2 (BM2) - A83-1 (MTT) Always 950 to 1050 Ω

    NG

    REPLACE BRAKE BOOSTER PUMP Click here

    OK

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


    1. Reconnect the brake booster pump connectors.

    2. Connect the intelligent tester to the DLC3.

    3. Turn the power switch on (IG).

    4. Select the Data List on the intelligent tester Click here.

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

      Accumulator pressure sensor /

      Min.: 0 V, Max.: 5 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, and check the output value on the intelligent tester with the motor stopped (not braking).

      OK
      Accumulator pressure sensor output voltage does not drop.

    NG

    PERFORM ACTIVE TEST USING INTELLIGENT TESTER (SOLENOID VALVE) Click here

    OK

    CHECK FOR INTERMITTENT PROBLEMS Click here

  4. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (SOLENOID VALVE)


    1. Turn the power switch off.

    2. Connect the intelligent tester to the DLC3.

    3. Turn the power switch on (IG).

    4. Select the Active Test on the intelligent tester Click here.

      Tech Tips

      The Active Test can be performed when the following conditions are met.


      • ABS main relays 1 and 2 are on.

      • Shift lever is in P.

      • Parking brake is applied.

      • Vehicle speed is 0 km/h (0 mph).

      ABS/VSC/TRC
      Tester Display Test Part Control Range Diagnostic Note
      ECB* Solenoid (SMC1) Master cut solenoid (SMC1) Solenoid ON/OFF Operation sound of solenoid (clicking sound) can be heard
      ECB* Solenoid (SMC2) Master cut solenoid (SMC2) Solenoid ON/OFF Operation sound of solenoid (clicking sound) can be heard
      ECB* Solenoid (SLRRL) Value Close Linear solenoid (RLR) valve Valve close ON/OFF Operation sound of solenoid (clicking sound) can be heard
      ECB* Solenoid (SLRRR) Value Close Linear solenoid (RRR) valve Valve close ON/OFF Operation sound of solenoid (clicking sound) can be heard

      *: Electronically Controlled Brake System

    5. Perform the Active Test of the solenoid using the intelligent tester.

      A01NF5ME02

    6. Select the Data List on the intelligent tester Click here.

      ABS/VSC/TRC
      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      FR W/C Sensor FR wheel cylinder pressure sensor / Min.: 0 V, Max.: 5 V When brake pedal is released: 0.3 to 0.7 V Reading increases when brake pedal is depressed
      FL W/C Sensor FL wheel cylinder pressure sensor / Min.: 0 V, Max.: 5 V When brake pedal is released: 0.3 to 0.7 V Reading increases when brake pedal is depressed
      RR W/C Sensor RR wheel cylinder pressure sensor / Min.: 0 V, Max.: 5 V When brake pedal is released: 0.3 to 0.7 V Reading increases when brake pedal is depressed
      RL W/C Sensor RL wheel cylinder pressure sensor / Min.: 0 V, Max.: 5 V When brake pedal is released: 0.3 to 0.7 V Reading increases when brake pedal is depressed

    7. Check that the output value of each wheel cylinder does not increase.

      OK
      The output value of each wheel cylinder does not increase.

      Tech Tips

      If any output value increases, there may be a brake fluid leak in the brake actuator.


    NG

    REPLACE BRAKE ACTUATOR ASSEMBLY Click here

    OK

    REPLACE BRAKE BOOSTER PUMP Click here