05–1053

DIAGNOSTICS – ELECTRONICALLY CONTOROLLED BRAKE SYSTEM 05IZM–01

DTC C1256/57 ACCUMULATOR LOW PRESSURE

CIRCUIT DESCRIPTION
The accumulator pressure sensor is built into the actuator and detects the accumulator pressure.
The skid control ECU turns on the Brake Control warning lamp and sounds the skid control buzzer if it senses
a decrease in the accumulator pressure.
DTC No. Detailed Code DTC Detecting Condition Trouble Area

Braking operation is input when
accumulator pressure is less
than 12.45 MPa and vehicle
speed is input (detected value
changes if accumulator pressure

Brake actuator assy (accumula-
is low after system start).
C1256/57 141 tor pressure, accumulator pres-

Accumulator pressure is less
sure sensor, pump motor)
than 14.62 MPa for 120 sec.
(changes according to power
source voltage) after system start
(stores the DTC after the condi-
tions are met, and drives buzzer).

Any of the wheel cylinder pres-
sure sensor value is lower than
the target value for at least 0.5
sec. when accumulator pressure
is less than 14.62 MPa and ve-
hicle speed is input.

Accumulator pressure changes
Brake actuator assy (accumula-
C1256/57 143 little when accumulator pressure tor pressure, accumulator pres-
is less than 14.62 MPa for at sure sensor, pump motor)
least 1 sec. without braking
(pump motor is operating).

Accumulator pressure is less
than 14.62 MPa for at least 0.5
sec. when motor relay is mal-
functioning.

2004 Prius – Preliminary Release (RM1075U)

Author: Date: 1217

05–1054
DIAGNOSTICS – ELECTRONICALLY CONTOROLLED BRAKE SYSTEM

INSPECTION PROCEDURE
HINT:
DTCs may be output if the accumulator pressure drops due to frequent braking (this is not a malfunction).
1 INSPECT BRAKE ACTUATOR ASSY

Brake Actuator Assy (a) Disconnect the brake actuator assy connector.
(b) Measure the resistance according to the value(s) in the
BM1 BM2
table below.
Standard:
Tester Connection Specified Condition
1 (BM2) – 31 (GND1) Below 10 Ω
2 (BM1) – 31 (GND1) Below 10 Ω
1 (BM2) – 2 (BM1) Below 1 Ω
GND1
MTT GND2 F47491
31 (GND1) – 32 (GND2) Below 1 Ω
1 (BM2) – 33 (MTT) About 10 Ω
2 (BM1) – 33 (MTT) About 10 Ω

NG REPLACE BRAKE ACTUATOR ASSY

OK

2 READ VALUE OF HAND–HELD TESTER

(a) Connect the hand–held tester to the DLC3.

(b) Turn the power switch ON (READY).
(c) Select the DATA LIST mode on the hand–held tester.
Measurement Item /
Item Normal condition
Range (Display)
Accumulator pressure sensor 1 / min.:
ACC PRESS SENS 1 Specified value: 3.2 to 4.0 V
0 V, max.: 5 V
(d) Depress the brake pedal 4 or 5 times to operate the pump motor, and check the output value on the
hand–held tester with the motor stopped (not braking).
OK:
ACC pressure sensor’s output voltage does not drop.
NG REPLACE BRAKE ACTUATOR ASSY
(SEE PAGE 32–54)

OK

REPLACE SKID CONTROL ECU ASSY (SEE PAGE 32–68)

NOTICE:
When replacing the skid control ECU assy, perform initialization of linear solenoid valve and calibra-
tion (see page 05–958).

2004 Prius – Preliminary Release (RM1075U)

Author: Date: 1218