DTC C1256: Accumulator Low Pressure [04/2018 -]: Procedure

WARNING: This page is about a different variant/trim than selected.

CHECK DTC

Clear the DTCs.
Refer to DTC CHECK / CLEAR [04/2018 -]

Chassis > ABS/VSC/TRAC > Clear DTCs
Turn the power switch off.
Turn the power switch on (IG).

Check if the same DTC is output.

Refer to DTC CHECK / CLEAR [04/2018 -]

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

Result:

REPAIR CIRCUITS INDICATED BY OUTPUT DTCS. Refer to DIAGNOSTIC TROUBLE CODE CHART [04/2018 - 08/2019] , or refer to DIAGNOSTIC TROUBLE CODE CHART [08/2019 - 08/2020] , or refer to DIAGNOSTIC TROUBLE CODE CHART [08/2020 - 08/2021] , or refer to DIAGNOSTIC TROUBLE CODE CHART [08/2021 -]

Result:

See step 2

INSPECT BRAKE BOOSTER PUMP ASSEMBLY

Turn the power switch off.

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

*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 connector.
OK

The connector is securely connected.
Disconnect the A40 brake booster pump assembly connector.
Check both the connector case and the terminals for deformation and corrosion.
OK

No deformation or corrosion.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
2 (BM1) - 4 (GND1)	Always	10 Ω or less
1 (BM2) - 3 (GND2)	Always	10 Ω or less
2 (BM1) - 1 (BM2)	Always	Below 1 Ω
4 (GND1) - 3 (GND2)	Always	Below 1 Ω

Result

Proceed to
OK
NG

Result:

REPLACE BRAKE BOOSTER PUMP ASSEMBLY. Refer to REMOVAL [04/2018 - 08/2021] , or refer to REMOVAL [08/2021 -]

Result:

See step 3

READ VALUE USING TECHSTREAM (ACCUMULATOR PRESSURE)

Reconnect the A40 brake booster pump assembly connector.
Disconnect the A34 brake pedal stroke sensor assembly connector.

Select the Data List on the Techstream.

Refer to DATA LIST / ACTIVE TEST [04/2018 -]

Chassis > ABS/VSC/TRAC > Data List

Tester Display	Measurement Item	Range	Normal Condition	Diagnostic Note
MT Voltage Value	MT voltage value	Min.: 0.00 V, Max.: 20.00 V	Pump motor off: 0.00 V Pump motor on: 12.00 V	-
Accumulator Pressure	Accumulator pressure output value	Min.: 0.00 MPa, Max.: 24.48 MPa	15.00 to 21.00 MPa (Pressure stable and pump motor stopped)	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
MT Voltage Value
Accumulator Pressure

Depress the brake pedal several times to operate the pump motor, then wait until it stops.

After the pump motor stops, wait for 30 seconds, then check the drop in the accumulator pressure sensor output value and the state of the pump motor.

Result

Result	Proceed to
The drop in the accumulator pressure sensor output value is less than 2.50 MPa 30 seconds after the pump motor stops, and the pump motor does not operate within 30 seconds after the pump motor stops.	A
The drop in the accumulator pressure sensor output value is 2.50 MPa or more 30 seconds after the pump motor stops, or the pump motor operates within 30 seconds after the pump motor stops.	B

Result:

USE SIMULATION METHOD TO CHECK. Refer to HOW TO PROCEED WITH TROUBLESHOOTING [04/2018 -]

Result:

See step 4

READ VALUE USING TECHSTREAM (SERVO PRESSURE)

Turn the power switch off.
Reconnect the A34 brake pedal stroke sensor assembly connector.

Select the Active Test on the Techstream.

Refer to DATA LIST / ACTIVE TEST [04/2018 -]

Chassis > ABS/VSC/TRAC > Active Test

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

Chassis > ABS/VSC/TRAC > Data List

Tester Display	Measurement Item	Range	Normal Condition	Diagnostic Note
Servo Pressure	Pressure value of servo	Min.: 0.00 MPa, Max.: 24.48 MPa	Brake pedal released: 0.00 to 2.10 MPa	Brake pedal is being depressed: Changes in proportion to the depression force of the brake pedal

Chassis > ABS/VSC/TRAC > Active Test

Active Test Display
ECB Solenoid (SLR)

Data List Display
Servo Pressure

Perform the Active Test and operate the linear solenoid (SLR) in the brake actuator (brake booster with master cylinder assembly).

Check that the servo pressure output value does not increase when performing the Active Test.

The servo pressure output value does not increase when performing the Active Test.

HINT:

If the servo pressure output value increases, an internal brake fluid leak in the brake actuator (brake booster with master cylinder assembly) is suspected.

Result

Result	Proceed to
The servo pressure output value increases.	A
The servo pressure output value does not increase.	B

Result:

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY. Refer to REMOVAL [04/2018 - 08/2021] , or refer to REMOVAL [08/2021 -]

Result:

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY AND BRAKE BOOSTER PUMP ASSEMBLY

for the brake booster with master cylinder assembly: Refer to REMOVAL [04/2018 - 08/2021] , or refer to REMOVAL [08/2021 -]

for the brake booster pump assembly: Refer to REMOVAL [04/2018 - 08/2021] , or refer to REMOVAL [08/2021 -]