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 brake actuator (brake booster with master cylinder assembly) and detects the accumulator pressure.

The skid control ECU (brake booster with master cylinder assembly) 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 stored if the accumulator pressure drops due to frequent braking (this is not a malfunction).

DTC No. Detection Item INF Code DTC Detection Condition Trouble Area Note
C1256/56 Accumulator Low Pressure 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 (Brake booster with master cylinder assembly)

  • Supply voltage reduced

 Electronically controlled brake system DTC

WIRING DIAGRAM

Refer to DTCs C1252/52 and C1253/53.

Click here

CAUTION / NOTICE / HINT

Note


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

    Click here

  • Inspect the fuses for circuits related to this system before performing the following procedure.

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.

for C1202/68: Click here

for C1241/41: Click here

for C1252/52 and C1253/53: Click here

for C1391/69: 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.

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

      Tech Tips

      This DTC may be stored even if the accumulator pressure drops only temporarily due to frequent braking.


    B

    END

    A

  2. INSPECT BRAKE BOOSTER PUMP ASSEMBLY


    1. A01KR90C07
      *a

      Component without harness connected

      (Brake Booster Pump Assembly)

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

    2. Disconnect the A126 and A127 brake booster pump assembly connectors.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A126-1 (BM1) - A126-2 (GND1) Always Below 10 Ω
      A127-2 (BM2) - A127-1 (GND2) Always Below 10 Ω
      A126-1 (BM1) - A127-2 (BM2) Always Below 1 Ω
      A126-2 (GND1) - A127-1 (GND2) Always Below 1 Ω
      Result
      Proceed to
      OK
      NG

    NG

    REPLACE BRAKE BOOSTER PUMP ASSEMBLY for LHD: Click here
    REPLACE BRAKE BOOSTER PUMP ASSEMBLY for RHD: Click here

    OK

  3. READ VALUE USING GTS (ACCUMULATOR PRESSURE SENSOR)


    1. Reconnect the A126 and A127 brake booster pump assembly 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


      Chassis > ABS/VSC/TRC > Data List
      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

      Chassis > ABS/VSC/TRC > Data List
      Tester Display
      Accumulator Sensor

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

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

      OK
      Accumulator pressure sensor output value change is less than 0.55 V.
      Result
      Proceed to
      OK
      NG

    OK

    USE SIMULATION METHOD TO CHECK Click here

    NG

  4. PERFORM ACTIVE TEST USING GTS (SOLENOID VALVE)


    1. Select the Active Test on the GTS.

      Click here


      Chassis > ABS/VSC/TRC > Active Test
      Tester Display Measurement Item 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

      • ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRC > Active Test
      Tester Display
      ECB Solenoid (SMC/SRC/SCC)

      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).

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

    3. Select the Data List on the GTS.

      Click here


      Chassis > ABS/VSC/TRC > Data List
      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 Brake pedal released: 0.10 to 0.90 V Reading increases when brake pedal is depressed

      Chassis > ABS/VSC/TRC > Data List
      Tester Display
      Wheel Cylinder Pressure Sensor

    4. Check that the output value of the wheel cylinder pressure sensor does not increase.

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

      Tech Tips

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

      Result
      Proceed to
      OK
      NG

    OK

    REPLACE BRAKE BOOSTER PUMP ASSEMBLY for LHD: Click here
    REPLACE BRAKE BOOSTER PUMP ASSEMBLY for RHD: Click here

    NG

    REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY for LHD: Click here
    REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY for RHD: Click here