DTC C1256/57: Accumulator Low Pressure: Procedure

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: Go to next step 

1. Make sure that there is no looseness at the locking part and the connecting part of the connectors.
   Fig 1: Identifying Brake Booster Pump Connectors

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
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
   A53-2 (BM1) - A53-4 (GND1)	Always	Below 10 Ω
   A54-2 (BM2) - A53-4 (GND1)	Always	Below 10 Ω
   A53-2 (BM1) - A54-2 (BM2)	Always	Below 1 Ω
   A53-4 (GND1) - A54-1 (GND2)	Always	Below 1 Ω
   A53-2 (BM1) - A53-1 (MTT)	Always	950 to 1050 Ω
   A54-2 (BM2) - A53-1 (MTT)	Always	950 to 1050 Ω

   TEXT IN ILLUSTRATION
   
   

   *1	Component without harness connected (Brake Booster Pump)

NG → See step   6 

OK: Go to next step 

1. Reconnect the brake booster pump connectors.
2. Connect the Techstream to the DLC3.
3. Turn the ignition switch to ON.
4. Select the Data List on the Techstream, refer to DATA LIST / ACTIVE TEST .
   ABS/VSC/TRAC
   
   

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   Accumulator Sensor	Accumulator pressure sensor / Min.: 0.00 V, Max.: 5.00 V	Specified value: 2.6 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. Wait for 30 seconds without operating the brake pedal. Then check the accumulator pressure sensor output value's change is within the specified range.

   OK

   Accumulator pressure sensor output value's change is within 0.2 V.

NG → See step   4 

OK → See step   5 

1. Turn the ignition switch off.
2. Connect the Techstream to the DLC3.
3. Turn the ignition switch to ON.
4. Select the Active Test on the Techstream, refer to DATA LIST / ACTIVE TEST .

   HINT: 

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

   • 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/TRAC
   
   

   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	-
   ECB* Solenoid (SLRRR) Value Close	Linear solenoid (RRR) valve	Valve close ON/OFF	-

   *: Electronically Controlled Brake System

5. Perform the Active Test of the solenoid using the Techstream.
   Fig 2: Identifying Brake Actuator Inner Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
6. Select the Data List on the Techstream, refer to DATA LIST / ACTIVE TEST .
   ABS/VSC/TRAC
   
   

   Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
   FR W/C Sensor	FR wheel cylinder pressure sensor / Min.: 0.00 V, Max.: 5.00 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.: 0.00 V, Max.: 5.00 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.: 0.00 V, Max.: 5.00 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.: 0.00 V, Max.: 5.00 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.

   HINT: 

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

NG → See step   7 

OK → See step   6