ELECTRONICALLY CONTROLLED BRAKE SYSTEM, Diagnostic DTC:C1256/56

DTC Code DTC Name
C1256/56 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 / red (malfunction) and brake warning light / yellow (minor malfunction), and sounds the meter buzzer if it senses a decrease in the accumulator pressure.

DTC C1256/56 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
C1256/56 341

Significant drop in accumulator pressure continues.

(DTCs will be stored and the buzzer will operate when either condition is met.)


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

  • Pump motor malfunction

  • Accumulator deterioration

  • Accumulator pressure sensor

  • Supply voltage reduced

WIRING DIAGRAM

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

CAUTION / NOTICE / HINT

Note

When replacing the brake booster with master cylinder (brake actuator), perform initialization and calibration of the linear solenoid valve Click here.

Tech Tips

When C1202/68, C1241/41, C1252/52, C1253/53 and/or C1391/69 are output together with C1256/56, inspect and repair the trouble areas indicated by C1202/68, C1241/41, C1252/52, C1253/53 and/or C1391/69 first (See page , , , 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
    A
  2. INSPECT BRAKE BOOSTER PUMP


    1. A005EW4E03
      Text in Illustration
      *a

      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
      A17-1 (BM1) - A17-2 (GND1) Always Below 10 Ω
      A18-2 (BM2) - A18-1 (GND2) Always Below 10 Ω
      A17-1 (BM1) - A18-2 (BM2) Always Below 1 Ω
      A17-2 (GND1) - A18-1 (GND2) Always Below 1 Ω

    NG
    OK
  3. READ VALUE USING GTS (ACCUMULATOR PRESSURE SENSOR)


    1. Reconnect the brake booster pump connectors.

    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: 2.90 to 4.20 V When brake fluid is stored in the accumulator: Accumulator pressure changes in accordance with volume of fluid stored in the accumulator
    5. Wait for 30 seconds without depressing the brake pedal.

    6. Check that the accumulator pressure sensor output values change is within the specified range.

      OK
      Accumulator pressure sensor output values change is within 0.55 V.

    OK
    NG
  4. PERFORM ACTIVE TEST USING GTS (SOLENOID VALVE)


    1. Select the Active Test on the GTS Click here.

      Tech Tips

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


      • ABS main relay is on.

      • Park (P) is selected.

      • 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 (SMC/SRC/SCC) Switching solenoid valve (SMC/SRC/SCC) Solenoid ON/OFF Operation sound of solenoid (clicking sound) can be heard

      *: Electronically Controlled Brake System

    2. Perform the Active Test of the solenoid using the GTS.

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

      ABS/VSC/TRC
      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Wheel Cylinder Pressure Sensor Wheel cylinder pressure sensor / Min.: 0.00 V, Max.: 5.00 V When brake pedal released: 0.10 to 0.90 V Reading increases when brake pedal is depressed
    4. Check that the output value of the wheel cylinder does not increase.

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

      Tech Tips

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

      Result
      Result Proceed to
      OK A
      NG (for LHD) B
      NG (for RHD) C

    A
    B
    C