Toyota Avalon (XX50): Abnormal Brake Pedal Response on First Depression. ABS does not Operate. ABS Operates Before Necessary When Braking

Toyota Avalon (XX50) 2019-2022 Service & Repair Manual / Brake / Brake Control / Dynamic Control Systems / Electronically Controlled Brake System(for Hv Model) / Abnormal Brake Pedal Response on First Depression. ABS does not Operate. ABS Operates Before Necessary When Braking

Abnormal Brake Pedal Response on First Depression

DESCRIPTION

If the vehicle has been stopped without opening or closing the driver door for a long period of time, the electronically controlled brake system will not be ready and sufficient fluid pressure may not be stored in the accumulator. In this case, the brake pedal response may not be the same as usual the first time the brake pedal is depressed. This is not a malfunction.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

After replacing the skid control ECU (brake booster with master cylinder assembly), perform linear solenoid valve offset learning, ABS holding solenoid valve learning, yaw rate and acceleration sensor zero point calibration and system information memorization after performing "Reset Memory".

Click here

PROCEDURE

1.	BRAKE PROBLEM CHECK

(a) Check the conditions at the time the problem occurred.

(1) Whether a warning light illuminated or the buzzer sounded.

(2) The number of times the power switch was turned on (IG) since the latest symptom occurred.

(3) Frequency of the symptom.

CHECK DTC

(a) Clear the DTCs.

Click here

Chassis > ABS/VSC/TRAC > Clear DTCs

(b) Turn the power switch off.

(d) Check the DTCs (electronically controlled brake system) that are output.

Click here

Chassis > ABS/VSC/TRAC > Trouble Codes

Result	Proceed to
DTCs C1391 and C1256 are not output.	A
DTCs C1391 and/or C1256 are output.	B

REPAIR CIRCUITS INDICATED BY OUTPUT DTCS

3.	CHECK VEHICLE

(a) Turn the power switch off.

(b) Depress the brake pedal within 2 minutes of opening the driver door and check the response of the brake pedal.

(c) Release the brake pedal and wait for 2 minutes without depressing the brake pedal, opening or closing the driver door or operating the power switch.

(d) After 2 seconds or more have elapsed, depress the brake pedal and check that the first depression response is different to successive depression responses.

HINT:

Compare the response of the brake pedal when the system is in sleep mode and when the stroke simulator is operating.

Result	Proceed to
The response of the brake pedal does not change.	A
The response of the brake pedal changed.	B

END

4.	INSPECT FRONT DOOR COURTESY LIGHT SWITCH ASSEMBLY LH

(a) Set the interior light door switch to ON and check that the map light assembly illuminates, then set the interior light door switch to DOOR.

(b) Check that the map light assembly illuminates when the driver door is opened.

OK:

The map light assembly illuminates when the driver door is opened.

INSPECT LIGHTING SYSTEM (COURTESY LIGHT SWITCH CIRCUIT)

5.	CHECK HARNESS AND CONNECTOR (CTY TERMINAL)

(a) Make sure that there is no looseness at the locking part and the connecting part of the connector.

OK:

The connector is securely connected.

*a	Front view of wire harness connector (to Skid Control ECU (Brake Booster with Master Cylinder Assembly))

(b) Disconnect the A35 skid control ECU (brake booster with master cylinder assembly) connector.

OK:

No deformation or corrosion.

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
A35-24 (CTY) - Body ground	Driver door open	1.5 V or less
A35-24 (CTY) - Body ground	Driver door closed	11 to 14 V

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR (CTY CIRCUIT)

ABS does not Operate

DESCRIPTION

When the electronically controlled brake system is operating, as the input piston and output piston are not directly connected, the kickback of the brake pedal is minimal during ABS operation and the driver may not notice that ABS operated.

CAUTION / NOTICE / HINT

NOTICE:

Click here

PROCEDURE

1.	BRAKE PROBLEM CHECK

(a) Check if the slip indicator light was illuminated or blinking when ABS did not operate.

HINT:

When the VSC system is normal and ABS is operating, the slip indicator light blinks.
When the VSC system is malfunctioning, the slip indicator light illuminates.

Result	Proceed to
The slip indicator light was blinking.	A
The slip indicator light was illuminated.	B

END

2.	CHECK DTC AND FREEZE FRAME DATA

(a) Using the Techstream, check DTCs and Freeze Frame Data.

Click here

Chassis > ABS/VSC/TRAC > Trouble Codes

Result	Proceed to
DTCs are not output.	A
DTCs are output.	B

REPAIR CIRCUITS INDICATED BY OUTPUT DTCS

3.	PERFORM OPERATION CHECK DRIVING

(a) Check that ABS operates using a drum tester or equivalent.

CAUTION:

When using a drum tester, enter Inspection Mode or VSC off mode and perform inspection with the TRAC and VSC systems disabled to prevent the vehicle from moving suddenly due to TRAC or VSC operation.

Click here

OK:

ABS operates.

END

REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY

ABS Operates Before Necessary When Braking

DESCRIPTION

Troubleshooting for when ABS operates too soon due to a noisy signal from the speed sensor, a difference in output, etc.

PROCEDURE

1.	PERFORM TEST MODE (SIGNAL CHECK) INSPECTION (SPEED SENSOR CIRCUIT)

(a) Using the Techstream, perform a Test Mode (Signal Check) inspection sensor check and check that speed sensor Test Mode (Signal Check) inspection items change from incomplete to complete.

Click here

Chassis > ABS/VSC/TRAC > Utility

Tester Display
Signal Check

OK:

Speed sensor Test Mode (Signal Check) inspection items change from incomplete to complete.

Result	Proceed to
OK (for Front)	A
OK (for Rear)	B
NG	C

NOTICE:

When cleaning the front speed sensor, make sure to clean the installation hole before installation.
Do not use parts cleaner when cleaning the front speed sensor rotor.

HINT:

The rear speed sensor and rear speed sensor rotor are incorporated into the rear axle hub and bearing assembly.

If the rear speed sensor and rear speed sensor rotor need to be replaced, replace the rear axle hub and bearing assembly.

CLEAN FRONT SPEED SENSOR AND FRONT SPEED SENSOR ROTOR

REPLACE REAR AXLE HUB AND BEARING ASSEMBLY

INSPECT AND REPAIR MALFUNCTIONING SPEED SENSOR CIRCUIT

Electronically Controlled Brake System(for Hv Model)

ABS Warning Light does not Come ON. ABS Warning Light Remains ON. Brake Actuator Operation Sound is Loud during Initial Check

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