AUTOHOLD

id041900702000

Outline

Caution

•  The AUTOHOLD function is a system which maintains the vehicle in a stopped condition using electronically controlled brake unit fluid pressure hold function. Because the function is not for enhancing the tire performance, the vehicle cannot be stopped if the grip limit of the tires is exceeded. Therefore, the function may not hold the vehicle on a steep or slippery road.

Function

AUTOHOLD display function

•  The AUTOHOLD display function notifies the driver of the system conditions using the AUTOHOLD operation indicator light, AUTOHOLD warning beep, and the multi-information display.

Structural View

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Hydraulic circuit diagram

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Block diagram

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Part name	Function
Electronically controlled brake unit	(See ELECTRONICALLY CONTROLLED BRAKE UNIT.)
PCM	(See PCM.)
SAS control module	(See SAS CONTROL MODULE [TWO-STEP DEPLOYMENT CONTROL SYSTEM - US/CANADA SPEC.].) (See SAS CONTROL MODULE [TWO-STEP DEPLOYMENT CONTROL SYSTEM (E)].)
Instrument cluster	(See INSTRUMENT CLUSTER [(E)].)
AUTOHOLD switch	(See AUTOHOLD SWITCH.)
AUTOHOLD operation indicator light	(See WARNING/INDICATION/ALARM [(E)].)
AUTOHOLD warning beep

Operation

AUTOHOLD control table

Control	Content
AUTOHOLD stand-by control	The AUTOHOLD function enters the AUTOHOLD stand-by condition when the AUTOHOLD switch is pressed with all of the AUTOHOLD operation conditions met, and the AUTOHOLD function becomes operable.
Electric parking brake request control	When the electric parking brake operation conditions are met during hold/pressure increase control, the electronically controlled brake unit sends an electric parking brake request signal to the electric parking brake control module, and operates the electric parking brake.
Hold/pressure increase control	The vehicle is held in the stopped position by maintaining/increasing the brake fluid pressure and operating the brake of each wheel.
Pressure decrease control	Decreases the brake fluid pressure and releases the brakes.
Drive-off control	Determines that the driver is attempting to accelerate the vehicle from a stop during hold/pressure increase control, and releases the brakes.

AUTOHOLD stand-by control

•  When the AUTOHOLD switch is pressed with all of the following conditions met, the AUTOHOLD stand-by indicator light turns on and AUTOHOLD becomes operable.

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―  AUTOHOLD stand-by indicator light is turned off

―  AUTOHOLD switch is normal

―  Driver’s seat belt is fastened

―  Driver's door is closed

―  Electronically controlled brake unit system is normal

―  Electric parking brake system is normal

•  When the AUTOHOLD switch is pressed again while the AUTOHOLD is not operating with the AUTOHOLD stand-by indicator light turned on, the AUTOHOLD indicator light turns off and the AUTOHOLD is disabled.

Note

•  If the AUTOHOLD switch is malfunctioning while the AUTOHOLD stand-by indicator light is turned on, the AUTOHOLD indicator light turns off and the AUTOHOLD is disabled.

Hold control

•  When all of the following conditions are met, the electronically controlled brake unit determines that the vehicle is stopped and performs hold control.

―  AUTOHOLD switch is on

―  Wheel speed is 0 km/h {0 mph}

―  Brake fluid pressure is specification or more after depressing brake pedal

―  Accelerator pedal is released

―  Electric parking brake system is normal

―  Electric parking brake is released

―  Electric parking brake switch is not operated

―  Driver seat belt is fastened

―  Driver's door is closed

―  Yaw rate is specification or less (vehicle is stopped)

―  Inclination of vehicle rear is approx. 5 % while the selector lever is in the R position, or the selector lever is in a position other than R.

•  When all of the operation conditions are met, the electronically controlled brake unit controls the linear actuator, maintains the brake fluid pressure and operates each wheel brake to stop the vehicle. In addition, the AUTOHOLD indicator light turns on.

•  If the driver forcefully depresses the brake pedal and the brake fluid pressure increases, the increased brake fluid is maintained. In addition, the electronically controlled brake unit continuously maintains hold control for a maximum of 10 min., and operates the electric parking brake.

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Pressure increase control

•  When all of the following conditions are met during AUTOHOLD operation, the electronically controlled brake unit performs pressure increase control.

―  Electronically controlled brake unit detects that vehicle moves

―  Brake pedal is released

―  Accelerator pedal is released

Electric parking brake request control

•  When any of the following conditions is met during hold/pressure increase control, the electronically controlled brake unit sends an electric parking brake request signal to the electric parking brake control module.(See ELECTRIC PARKING BRAKE [(E)].)

―  Main power OFF

―  Driver seat belt is unfastened

―  Driver's door is opened from closed condition

―  Approx. 10 min. or more have elapsed from start of hold/pressure increase control

―  Electric parking brake is normal and vehicle is moving even if pressure increase control is performed

―  Malfunction occurs in electronically controlled brake unit and continuous hold is not possible or difficult

―  Malfunction occurred in AUTOHOLD system

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•  When the brake fluid pressure is reduced, the AUTOHOLD operation indicator light turns off.

Note

•  For the electric parking brake release conditions, refer to [ELECTRIC PARKING BRAKE] (electric parking brake release and electric parking brake automatic release).(See ELECTRIC PARKING BRAKE [(E)].)

Pressure decrease control

•  When all of the following conditions are met during hold/pressure increase control, the electronically controlled brake unit determines that it is not necessary to operate AUTOHOLD and reduces the brake fluid pressure.

―  Electric parking brake is operated

―  The driver selects the R position and the electronically controlled brake unit determines that the vehicle is on a flat road or the inclination of the front of the vehicle is approx. 5 % based on the longitudinal-G signal sent from the SAS control module.

―  Accelerator pedal is fully depressed

•  When the brake fluid pressure is reduced, the AUTOHOLD indicator light turns off.

Drive-off control

•  When any of the following conditions is met with the main power switched ON (READY on) during hold/pressure increase control, the electronically controlled brake unit determines that the driver is attempting to accelerate the vehicle from a stop and performs drive-off control.

Driving on a flat road

―  D position is selected and accelerator pedal is depressed to specification or more

Vehicle front pitched upward

―  D position is selected and drive torque required for acceleration occurs by accelerator pedal operation

Vehicle front pitched downward

―  D position is selected and accelerator pedal is depressed to specification or more

―  R position is selected and drive torque required for acceleration occurs by accelerator pedal operation

•  If the motor torque signal sent from the PCM is the specification or more, the electronically controlled brake unit determines that the vehicle can be accelerated from the stop and decreases the brake fluid pressure. The time under which brake fluid pressure reduction is performed changes depending on the longitudinal-G signal (slope) sent from the SAS control module.

•  When the brake fluid pressure is reduced, the AUTOHOLD operation indicator light turns off.

System malfunctioning

Electronically controlled brake system malfunction

•  If the hold/pressure increase control cannot be performed due to a malfunction in the electronically controlled brake system, the electronically controlled brake unit performs the following controls.

AUTOHOLD switch off

―  Inhibits the AUTOHOLD.

AUTOHOLD switch is on

During AUTOHOLD non-operation

•  Inhibits the AUTOHOLD.

During hold/pressure increase control

•  The electronically controlled brake unit sends an electric parking brake request signal immediately. When the electric parking brake operates, the electronically controlled brake unit inhibits the AUTOHOLD after reducing the maintained brake fluid pressure.

Note

•  If a malfunction occurs in the electronically controlled brake system and a malfunction in the electric parking brake at the same time, the brake fluid pressure may be reduced without switching to the electric parking brake. At this time, the AUTOHOLD warning beep request signal is sent to the BCM.

During drive-off control and pressure reduction control for certain period of time

•  Inhibits the AUTOHOLD after the brake fluid pressure reduction is completed.

Electric parking brake system malfunction

•  If there is a malfunction in the electric parking brake, the electronically controlled brake unit performs the following controls.

AUTOHOLD switch off

―  Inhibits the AUTOHOLD.

AUTOHOLD switch is on

During AUTOHOLD non-operation

•  Inhibits the AUTOHOLD.

During hold/pressure increase control

―  Inhibits the AUTOHOLD after the drive-off control is completed.

―  The electronically controlled brake unit sends an AUTOHOLD warning beep request signal to the BCM via CAN communication.

―  When the BCM receives the AUTOHOLD warning beep request signal, the AUTOHOLD warning beep is activated from the notification and warning speaker.(See WARNING/INDICATION/ALARM [(E)].)

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AUTOHOLD display function

•  The AUTOHOLD display function notifies the driver of the system conditions using the AUTOHOLD operation indicator light, and multi-information display.

•  When the AUTOHOLD is operating or the AUTOHOLD switch is operated while the AUTOHOLD is not operating even if a malfunction occurs in the AUTOHOLD function and the AUTOHOLD switch is operated, the driver is alerted by the warning light flashing, message indication, and a warning beep is activated for 5 s.

Status	AUTOHOLD operation indicator light	Multi-information display
AUTOHOLD is operating	ON	—
System related to brake is malfunctioning while vehicle is stopped by AUTOHOLD function operation	Flash
There is the possibility that the vehicle cannot be maintained in a stopped condition on steep slope by AUTOHOLD operation	Flash
Cancellation is operated without depressing brake pedal while vehicle is stopped by AUTOHOLD function operation	ON
Door is open or seat belt is not fastened during AUTOHOLD operation	OFF