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Home >> Lexus >> 2020 >> LC 500 >> Repair and Diagnosis >> Brakes >> Mechanical - Hydraulic >> Electronically Controlled Brake System - Diagnostic Codes (Coupe) (2 Of 4) >> Electronically Controlled Brake System >> DTC C1256: Accumulator Low Pressure [09/2018 - ] >> Procedure

DTC C1256: Accumulator Low Pressure [09/2018 - ]: Procedure

  1. CHECK DTC 
    1. Check if the same DTC is output.

      Refer to DTC CHECK / CLEAR [09/2018 - ]

      Chassis > ABS/VSC/TRAC > Trouble Codes 

      Result

      Result Proceed to
      DTC C1256 is output. A
      DTCs C1202, C1241, C1252, C1253 and/or C1391 are output. B

      HINT: 

      • External brake fluid leaks are suspected if C1202 is output.
      • An external brake fluid leak or an internal leak in the accumulator is suspected if C1391 is output.

    Result: 

    B 

    REPAIR CIRCUITS INDICATED BY OUTPUT DTCS. Refer to  DIAGNOSTIC TROUBLE CODE CHART [09/2018 - 05/2023]  , or refer to  DIAGNOSTIC TROUBLE CODE CHART [05/2023 - ] 

    Result: 

    A 

    See step  2

  2. 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

      HINT: 

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

    Result: 

    B 

    END 

    Result: 

    A 

    See step  3

  3. INSPECT BRAKE BOOSTER WITH ACCUMULATOR PUMP ASSEMBLY 
    1. Make sure that there is no looseness at the locking part and the connecting part of the connectors.
      GTY809473Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
      *a Component without harness connected
      (Brake Booster with Accumulator Pump Assembly)
    2. Disconnect the A48 and A49 brake booster with accumulator pump assembly connectors.
    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection Condition Specified Condition
      A48-2 (BM1) - A48-4 (GND1) Always Below 10 Ω
      A49-2 (BM2) - A49-1 (GND2) Always Below 10 Ω
      A48-2 (BM1) - A49-2 (BM2) Always Below 1 Ω
      A48-4 (GND1) - A49-1 (GND2) Always Below 1 Ω
      A48-2 (BM1) - A48-1 (MTT) Always 950 to 1050 Ω
      A49-2 (BM2) - A48-1 (MTT) Always 950 to 1050 Ω

      Result

      Proceed to
      OK
      NG

    Result: 

    NG 

    REPLACE BRAKE BOOSTER WITH ACCUMULATOR PUMP ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

    Result: 

    OK 

    See step  4

  4. READ VALUE USING TECHSTREAM (ACCUMULATOR PRESSURE SENSOR) 
    1. Reconnect the A48 and A49 brake booster with accumulator pump assembly connectors.
    2. Connect the Techstream to the DLC3.
    3. Turn the engine switch on (IG).
    4. Select the Data List on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [03/2017 - 05/2023] , or refer to DATA LIST / ACTIVE TEST [05/2023 - ]

      Chassis > ABS/VSC/TRAC > 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: 2.60 to 3.80 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/TRAC > Data List 

      Tester Display
      Accumulator Sensor
    5. Depress the brake pedal 4 or 5 times and operate the pump motor.
    6. Wait for 30 seconds without depressing the brake pedal.
    7. Check that the accumulator pressure sensor output value change is within the specified range.

      OK

      Accumulator pressure sensor output value change is less than 0.20 V.

      HINT: 

      • This inspection is performed to determine if a long-term power malfunction occurred when low pressure is detected due to a defective sensor, an internal leak in the brake actuator assembly, or deterioration of the accumulator.
      • External brake fluid leaks are suspected if the fluid level drops inside the brake master cylinder reservoir assembly.

      Result

      Proceed to
      OK
      NG

    Result: 

    OK 

    USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [03/2017 - 04/2020]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [04/2020 - 05/2023]  , or refer to  HOW TO PROCEED WITH TROUBLESHOOTING [05/2023 - ] 

    Result: 

    NG 

    See step  5

  5. PERFORM ACTIVE TEST USING TECHSTREAM (SOLENOID VALVE) 
    1. Turn the engine switch off.
    2. Connect the Techstream to the DLC3.
    3. Turn the engine switch on (IG).
    4. Select the Active Test on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [03/2017 - 05/2023] , or refer to DATA LIST / ACTIVE TEST [05/2023 - ]

    5. With the brake pedal released, set "ECB Solenoid (SMC1)" to "ON" and check the output voltage of "FR W/C Sensor".
      1. ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      ECB Solenoid (SMC1) Master cut solenoid (SMC1) Solenoid ON/OFF ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      FR W/C Sensor Front wheel cylinder pressure sensor RH Min.: 0.00 V, Max.: 5.00 V Brake pedal released: 0.30 to 0.70 V Reading increases when brake pedal is depressed

      Chassis > ABS/VSC/TRAC > Active Test 

      Active Test Display
      ECB Solenoid (SMC1)
      Data List Display
      FR W/C Sensor
      1. ECB: Electronically Controlled Brake System

      OK

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

      HINT: 

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

      Result

      Result Proceed to
      The output values of the wheel cylinder pressure sensors do not increase. A
      The output value of the wheel cylinder pressure sensor increases. B

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

    Result: 

    A 

    See step  6

  6. PERFORM ACTIVE TEST USING TECHSTREAM (SOLENOID VALVE) 
    1. Turn the engine switch off.
    2. Connect the Techstream to the DLC3.
    3. Turn the engine switch on (IG).
    4. Select the Active Test on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [03/2017 - 05/2023] , or refer to DATA LIST / ACTIVE TEST [05/2023 - ]

    5. With the brake pedal released, set "ECB Solenoid (SMC2)" to "ON" and check the output voltage of "FL W/C Sensor".
      1. ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      ECB Solenoid (SMC2) Master cut solenoid (SMC2) Solenoid ON/OFF ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      FL W/C Sensor Front wheel cylinder pressure sensor LH Min.: 0.00 V, Max.: 5.00 V Brake pedal released: 0.30 to 0.70 V Reading increases when brake pedal is depressed

      Chassis > ABS/VSC/TRAC > Active Test 

      Active Test Display
      ECB Solenoid (SMC2)
      Data List Display
      FL W/C Sensor
      1. ECB: Electronically Controlled Brake System

      OK

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

      HINT: 

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

      Result

      Result Proceed to
      The output values of the wheel cylinder pressure sensors do not increase. A
      The output value of the wheel cylinder pressure sensor increases. B

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

    Result: 

    A 

    See step  7

  7. PERFORM ACTIVE TEST USING TECHSTREAM (SOLENOID VALVE) 
    1. Turn the engine switch off.
    2. Connect the Techstream to the DLC3.
    3. Turn the engine switch on (IG).
    4. Select the Active Test on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [03/2017 - 05/2023] , or refer to DATA LIST / ACTIVE TEST [05/2023 - ]

    5. With the brake pedal released, set the current of "ECB Solenoid (SLRRR)" to 1.2 A and check the output voltage of "RR W/C Sensor".
      1. ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      ECB Solenoid (SLRRR) Linear solenoid (RRR) valve Solenoid ON/OFF ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      RR W/C Sensor Rear wheel cylinder pressure sensor RH Min.: 0.00 V, Max.: 5.00 V Brake pedal released: 0.30 to 0.70 V Reading increases when brake pedal is depressed

      Chassis > ABS/VSC/TRAC > Active Test 

      Active Test Display
      ECB Solenoid (SLRRR)
      Data List Display
      RR W/C Sensor
      1. ECB: Electronically Controlled Brake System

      OK

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

      HINT: 

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

      Result

      Result Proceed to
      The output values of the wheel cylinder pressure sensors do not increase. A
      The output value of the wheel cylinder pressure sensor increases. B

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

    Result: 

    A 

    See step  8

  8. PERFORM ACTIVE TEST USING TECHSTREAM (SOLENOID VALVE) 
    1. Turn the engine switch off.
    2. Connect the Techstream to the DLC3.
    3. Turn the engine switch on (IG).
    4. Select the Active Test on the Techstream.

      Refer to DATA LIST / ACTIVE TEST [03/2017 - 05/2023] , or refer to DATA LIST / ACTIVE TEST [05/2023 - ]

    5. With the brake pedal released, set the current of "ECB Solenoid (SLRRL)" to 1.2 A and check the output voltage of "RL W/C Sensor".
      1. ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Active Test 

      Tester Display Measurement Item Control Range Diagnostic Note
      ECB Solenoid (SLRRL) Linear solenoid (RLR) valve Solenoid ON/OFF ECB: Electronically Controlled Brake System

      Chassis > ABS/VSC/TRAC > Data List 

      Tester Display Measurement Item Range Normal Condition Diagnostic Note
      RL W/C Sensor Rear wheel cylinder pressure sensor LH Min.: 0.00 V, Max.: 5.00 V Brake pedal released: 0.30 to 0.70 V Reading increases when brake pedal is depressed

      Chassis > ABS/VSC/TRAC > Active Test 

      Active Test Display
      ECB Solenoid (SLRRL)
      Data List Display
      RL W/C Sensor
      1. ECB: Electronically Controlled Brake System

      OK

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

      HINT: 

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

      Result

      Result Proceed to
      The output values of the wheel cylinder pressure sensors do not increase. A
      The output value of the wheel cylinder pressure sensor increases. B

    Result: 

    A 

    REPLACE BRAKE BOOSTER WITH ACCUMULATOR PUMP ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

    Result: 

    B 

    REPLACE BRAKE ACTUATOR ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]  , or refer to  REMOVAL [05/2023 - ] 

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