Toyota 4Runner manuals

Toyota 4Runner: Accumulator Low Pressure (C1256)

DESCRIPTION

Refer to DTC C1254 (See page ).


DTC Code

DTC Detection Condition

Trouble Area

C1256

The fluid pressure inside the accumulator is below the standard value.

  • Brake booster with accumulator pump assembly
  • Master cylinder solenoid (Accumulator pressure sensor)
  • Hydraulic brake booster assembly

CAUTION / NOTICE / HINT

NOTICE:

When replacing the master cylinder solenoid, perform calibration (See page ).


HINT:

When DTC C1251, C1253 or C1254 is output together with DTC C1256 inspect and repair the trouble area indicated by DTC C1251, C1253 or C1254 first.

PROCEDURE

1.

RECONFIRM DTC

(a) Clear the DTCs (See page ).


(b) Turn the ignition switch off.

(c) Depress the brake pedal 20 times or more.

(d) Turn the ignition switch to ON.

(e) Wait for 99 seconds.

(f) Check if the same DTC is output (See page
).

Result

Result

Proceed to

DTC is output

A

DTC is not output

B

HINT:

Excessive brake pedal operation results in abnormal accumulator pressure consumption. This is normal.


B

USE SIMULATION METHOD TO CHECK

A

2.

INSPECT HYDRAULIC BRAKE BOOSTER ASSEMBLY FUNCTION

(a) Inspect brake booster pump power supply system function.

(1) Turn the ignition switch off.

(2) Depress the brake pedal 20 times or more to release the pressure in the accumulator.

HINT:

When the pressure is released, the brake pedal stroke becomes longer.

(3) Check that the brake fluid level is at the MAX level.

(4) Chock the 4 wheels and release the parking brake.

(5) Turn the ignition switch to ON and measure the brake booster pump operating time (the time from when the brake booster pump starts operating until it stops).

OK:

20 to 80 seconds

(6) Start the engine after the brake boost pump stops.

(7) Check that the ABS warning light and slip indicator light are not illuminated.

(8) Turn off the engine, and then turn the ignition switch to ON.

(9) Check that the brake boost pump operates and then stops when the brake pedal is depressed 4 or 5 times.

(10) Depress the brake pedal 4 or 5 times and measure the brake booster pump operating time (the time from when the brake booster pump starts operating until it stops).

OK:

2 to 11 seconds

(11) Check that the brake warning light illuminates and the buzzer sounds when the brake pedal is fully depressed continuously 15 to 20 times.

NOTICE:

Wait 120 seconds or more after turning the ignition switch to ON before performing this inspection.

(b) Check brake booster operation.

(1) Turn the ignition switch off.

(2) Depress the brake pedal 20 times or more to release the pressure in the accumulator.

HINT:

When the pressure is released, the brake pedal stroke becomes longer.

(3) Depress the brake pedal, start the engine, and check the change in the brake pedal height.

OK:

The brake pedal moves slightly inward.

(c) Inspect brake master cylinder fluid pressure change (See page ).



NG

GO TO STEP 5

OK

3.

READ VALUE USING TECHSTREAM (ACCUMULATOR SENSOR)

(a) Turn the ignition switch off.

(b) Connect the Techstream to the DLC3.

(c) Turn the ignition switch to ON.

(d) Turn the Techstream on.

(e) Enter the following menus: Chassis / ABS/VSC/TRAC / Data List.

ABS/VSC/TRAC

Tester Display

Measurement Item/Range

Normal Condition

Diagnostic Note

Accumulator Sensor

Accumulator pressure sensor reading/ Min.: 0.00 V, Max.: 5.00 V

3.58 to 5 V

If the value is constant regardless of the pump operation, an accumulator pressure sensor malfunction is suspected.

(f) Check that the accumulator output value is normal.

OK:

Accumulator pressure sensor value is normal.


NG

REPLACE MASTER CYLINDER SOLENOID

OK

4.

RECONFIRM DTC

(a) Clear the DTCs (See page ).


(b) Turn the ignition switch off.

(c) Check if the same DTC is output (See page
).

Result

Result

Proceed to

DTC is output

A

DTC is not output

B


A

REPLACE MASTER CYLINDER SOLENOID


B

USE SIMULATION METHOD TO CHECK

5.

INSPECT BRAKE BOOSTER PUMP ASSEMBLY

(a) Remove the hydraulic brake booster assembly (See page ).


(b) Using a screwdriver, remove the 2 screws and pull out the wire harness from the master cylinder solenoid.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Red wire terminal - Black wire terminal

Always

Below 2 Ω

Text in Illustration

*1

Pump motor wire harness

*a

Red wire

*b

Black wire


(d) Install the pump motor wire harness to the master cylinder solenoid with the 2 screws.

Torque:

2.9 N·m {30 kgf·cm, 26 in·lbf}


OK

REPLACE HYDRAULIC BRAKE BOOSTER ASSEMBLY


NG

REPLACE BRAKE BOOSTER WITH ACCUMULATOR PUMP ASSEMBLY

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