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DTC    C1256/56    Accumulator Low Pressure

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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 skid control 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.)
  1. Accumulator pressure dropped due to frequent brake pedal operation (not a malfunction)
  2. Pump motor malfunction
  3. Accumulator deterioration
  4. Accumulator pressure sensor
  5. Supply voltage reduced

WIRING DIAGRAM

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

INSPECTION PROCEDURE

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

HINT:
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 (Click here, Click here, Click here, or Click here).

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

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



B
END
A


2.INSPECT BRAKE BOOSTER PUMP


    C156574E01

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

  1. Disconnect the brake booster pump connectors.

  1. 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

    Text in Illustration 
    *1
    		Component without harness connected
    (Brake Booster Pump)



NG
REPLACE BRAKE BOOSTER PUMP (Click here)
OK


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

  1. Reconnect the brake booster pump connectors.

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. 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: 2.9 to 4.2 V
    		When brake fluid is stored in the accumulator: Accumulator pressure changes in accordance with volume of fluid stored in the accumulator

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

  1. 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.



NG
Go to step 4
OK

CHECK FOR INTERMITTENT PROBLEMS (Click here)  

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

  1. Turn the power switch off.

  1. Connect the intelligent tester to the DLC3.

  1. Turn the power switch on (IG).

  1. Select the Active Test on the intelligent tester (Click here).

    HINT:
    The Active Test can be performed when the following conditions are met.
    1. ABS main relay is on.
    2. Park (P) selected.
    3. Parking brake is applied.
    4. 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

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

  1. Select the Data List on the intelligent tester (Click here).


ABS/VSC/TRC 
Tester Display
Measurement Item/Range
Normal Condition
Diagnostic Note
Wheel Cylinder Pressure Sensor
Wheel cylinder pressure sensor / Min.: 0 V, Max.: 5 V
When brake pedal released: 0.1 to 0.9 V
Reading increases when brake pedal is depressed

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

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

    HINT:
    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



B
REPLACE BRAKE BOOSTER WITH MASTER CYLINDER (Click here)

C
REPLACE BRAKE BOOSTER WITH MASTER CYLINDER (Click here)
A

REPLACE BRAKE BOOSTER PUMP (Click here)