Infiniti FX35, FX50 (S51). Manual - part 1587

SBC-6

< SYSTEM DESCRIPTION >

PRE-CRASH SEAT BELT SYSTEM

SYSTEM DESCRIPTION

PRE-CRASH SEAT BELT SYSTEM

System Diagram

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System Description

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• Pre-crash seat belt system (with comfort function) is adopted for driver and passenger seat belts.
• Pre-crash seat belt system integrates control unit and motor in driver and passenger seat belt retractors.
• Provides a sense of ease when pre-crash seat belt control unit judges the emergency braking operation, the

intelligent brake assistance operating status, the continuous ABS operating status, the emergency steering
wheel operation, or the lateral slippage status during cornering, the motor immediately retracts the seat belt
and suppresses change in occupant posture.

• Even in a situation where a collision is unavoidable, effects of other safety devices, like the air bag, are max-

imized and damages are reduced.

• Motor retracts seat belt when unfastening and extracts seat belt when fastening to reduce the feeling of

pressure.(comfort function) 

FUNCTION DESCRIPTION

Pre-crash seat belt system operates under the following conditions.
• During emergency brake operation
• When ABS continuously operates
• When intelligent brake assistance operates
• When lateral slippage during cornering occurs
• When steering wheel is rotated for emergency
• When comfort function operates

OPERATION CONDITION

Operation start and stop conditions of pre-crash seat belt system are as shown in the following table.

JMHIA1403GB

PRE-CRASH SEAT BELT SYSTEM

SBC-7

< SYSTEM DESCRIPTION >

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D

E

F

G

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J

K

L

M

A

B

SBC

N

O

P

Operation starts when all of the operation start conditions are satisfied and operation stops when  any one of
the stop conditions is satisfied.

NOTE:
For details of intelligent brake assist system.Refer to 

BRC-144, "System Description"

.

Comfort function

• Seat belt is retracted and the looseness is reduced in the state as shown in the following table.
• Operation starts when all of the operation start conditions are satisfied and operation stops when  any one of

the stop conditions is satisfied.

Operation Prohibition Condition

Pre-crash seat belt system does not operate in the following conditions.
• When seat belt is not fastened (Only the seat belt that is not fastened does not operate)
• When motor is overheat due to contentious operation*1
• When the system is in fail-safe mode

*1: System operation is temporarily deactivated to avoid overheating, when comfort function is continuously
operated (18 times or more) during a short period of time by fastening and unfastening seat belts or opening
and closing doors.

MALFUNCTION WARNING

When system malfunction is detected, comfort function is deactivated to warn customer of system malfunc-
tion.  

Operation item

Operation start condition

Operation stop condition

During emergency brake operation

• Emergency braking status is detected
• Vehicle speed is 15 km/h (9 MPH) or more

• During acceleration
• When stopped

When ABS continuously operates

• ABS continuously operates for 2 seconds or 

more

• Brake pedal is in depressed state

When intelligent brake assistance oper-
ates

System detects that intelligent brake assistance is 
in operating status

2 seconds after operation start

When lateral slippage during cornering 
occurs

• Vehicle speed is 30 km/h (19 MPH) or more
• System detects that the vehicle is in lateral slip-

page state

• System detects that the vehicle is driving on a 

curve

• Vehicle stopped
• 1 second or more after maintaining 

steering wheel angle in straight driv-
ing state

When steering wheel is rotated for emer-
gency

• Vehicle speed is 60 km/h (36 MPH) or more
• Steering wheel angle is 90 degrees or more
• System detects that steering wheel is rotated for 

emergency

Activating condition

Deactivating condition

Door open

• Seat belt not installed condition
• Door is operated to open from close
• Vehicle stopped

• Seat belt retract is complete
• 13 seconds after start retracting

Seat belt is fastened

• When door is closed
• Seat belt is fastened

• Seat belt is unfastened
• 1 second after operation

Seat belt is released

Seat belt is unfastened

• Seat belt retract is complete
• 10 seconds after start retracting

SBC-8

< SYSTEM DESCRIPTION >

PRE-CRASH SEAT BELT SYSTEM

Component Parts Location

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1.

ICC sensor integrated unit  

2.

ABS actuator and electric unit (con-
trol unit)

3.

Steering angle sensor Pre-crash

4.

Seat belt buckle switch (driver side) 

5.

Seat belt buckle switch (passenger 
side) 

6.

Unified meter and A/C amp.

7.

BCM

8.

Brake  pedal  stroke  sensor

9.

Pre-crash seat belt control unit (driver 
side)

10.

 seat belt control unit (passenger 
side) 

A.

View with instrument driver lower 
cover removed

B.

View with center pillar lower garnish 
removed (driver side)

C.

View with center pillar lower garnish 
removed (passenger side)

JMHIA1406ZZ

PRE-CRASH SEAT BELT SYSTEM

SBC-9

< SYSTEM DESCRIPTION >

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D

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F

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K

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A

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Component Description

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Component

Function

Pre-tensioner seat belt with pre-crush control 
unit built in motor

• It controls pre-crash seat belt motor according to input signal.
• It is built into seat belt retractor, and it pulls, returns, and maintains according 

to the motor rotation.

Brake pedal stroke sensor

• It changes voltage according to brake pedal depressed amount and sends the 

signal to pre-crash seat belt control unit.

• There are 2 signals (brake pedal stroke sensor 1 and 2) sent from the brake 

pedal stroke sensor. Pre-crash seat belt control unit judges the stroke amount 
and the speed of the brake pedal according to the voltage of the signal sent by 
each side.

Seat belt buckle switch

It is arranged in the seat belt buckle and judges whether the seat belt is fastened 
or not fastened.

CAN system
• Unified meter and A/C amp
• BCM
• Steering angle sensor
• ABS actuator and electric unit (control unit)

It transmits the vehicle status to pre-crash seat belt control unit using the CAN 
communication system.