LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2008 >> IS F >> Repair and Diagnosis >> Restraints >> Air Bag, SRS >> Pre-Collision >> Pre-Collision System >> System Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

System Description

  1. PRE-COLLISION SYSTEM 
    1. The pre-collision system optimizes and activates occupant protection equipment (see below) to attempt to reduce damage due to a collision.
  2. OUTLINE OF PRE-COLLISION SYSTEM 
    PRE-COLLISION SYSTEM OPERATION CHART

    Operating Condition Control Transmitting ECU Receiving ECU Part Operated
    Operates according to sensor detection Pre-collision seat belt Distance control ECU Seat belt control ECU Front seat outer belts
    Operates according to sensor detection Pre-collision brake assist Distance control ECU Skid control ECU Brake assist system
    Operates when sudden braking occurs Pre-collision seat belt Skid control ECU Seat belt control ECU Front seat outer belts
    1. When operating according to sensor detection: The millimeter wave radar sensor detects vehicles and other objects on the road in front of the user's vehicle. The distance control ECU determines if a collision is unavoidable based on object position, speed and track information. If the distance control ECU determines that a collision is unavoidable, it transmits this information to the following areas using CAN communication:
      • Seat belt control ECU (initiates control of pre-collision seat belts)
      • Skid control ECU (activates pre-collision brake assist system)
    2. When operating as a result of sudden braking: The skid control ECU uses brake pressure information and other data to determine if the driver has suddenly applied the brakes. If so, the skid control ECU sends a signal to the seat belt control ECU through CAN communication and the pre-collision seat belt activates.
  3. OUTLINE OF PRE-COLLISION SEAT BELT CONTROL 
    1. The pre-collision seat belt operates depending on what the sensor detects, or whether sudden braking has occurred. The pre-collision seat belt motor tightens the seat belt to optimize occupant restraint performance.
    2. Operative condition
      1. Refer to the sensor and sudden braking descriptions under  2"Outline of Pre-Collision System" (see above)
  4. OUTLINE OF PRE-COLLISION BRAKE ASSIST CONTROL 
    1. The pre-collision brake assist operates depending on what the sensor detects. The system then enters standby mode before a collision When the driver depresses the brake pedal, brake fluid pressure is increased to improve fluid pressure response and improve vehicle speed reduction rate.
    2. Operative condition
      1. Refer to the sensor description under  2"Outline of Pre-Collision System" (see above).
      2. When the driver depresses the brake pedal after the distance control ECU determines that a collision is unavoidable:

        Brake fluid pressure is increased at the same time the driver depresses the brake pedal.

      3. When the driver depresses the brake pedal before the distance control ECU determines that a collision is unavoidable:

        Brake fluid pressure is increased at the same time that the distance control ECU receives a pre-collision sensor signal (indicating that other vehicles or objects are in front of the vehicle).

  5. OPERATIVE CONDITION AND INOPERATIVE CONDITION OF EACH CONTROL (REVIEW) 
    OPERATIVE CONDITION AND INOPERATIVE CONDITION

      Pre-Collision Seat Belt(1) Pre-Collision Seat Belt(2) Pre-Collision Brake Assist(2)
    Engine switch off or on (ACC) - - -
    When a warning message is displayed on the multi-information display (3) (3) (3)
    When seat belt(s) is/are fastened (4) (4) ◦
    Operates when the vehicle speed is 30 km/h (18 mph) or more, regardless of relative speed ◦ - -
    Operates when the vehicle speed is 5 km/h (3 mph) or more and relative speed is 30 km/h (18 mph) - ◦ -
    Operates when the vehicle speed is 30 km/h (18 mph) or more and relative speed is 30 km/h (18 mph) - - ◦
    When the vehicle collides with an object outside the detection range of the millimeter wave radar sensor (side collision, rear collision, etc) ◦ - -
    When the millimeter wave radar sensor cannot detect a possible collision object ◦ - -
    (1) Operates when brakes are suddenly applied.
    (2) Operates according to sensor detection.
    (3) Inoperative parts are different depending on malfunction areas
    (4) Only operates when seat belt is fastened
    ◦. Main basis for operation
    -. Does not operate, or not main basis for operation
  6. PRECAUTION FOR PRE-COLLISION SYSTEM OPERATION 
    1. When the millimeter wave radar sensor detects an object in front of the vehicle under the conditions described below, the distance control ECU may determine that a collision is unavoidable, and activate the pre-collision system This activation of the system is not abnormal.
      Fig 1: Pre-Collision System Operation Chart
      G05754805Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

      HINT

      • The pre-collision system will not activate when the pre-collision sensor detects safety cones and other plastic objects
      • The pre-collision system may or may not activate when the pre-collision sensor detects the following objects people, bicycles, motorcycles, trees, animals and snow fences.
      PRE-COLLISION SYSTEM REFERENCE

      Object Type Example
      Objects that cannot be detected Plastic items (safety cones)
      Objects that cannot be detected in a stable manner People, bicycles, motorcycles, trees, animals, snow fences, etc
scientia non olet · About LEMON Manuals