System Description

1. The pre-collision system optimizes and activates occupant protection equipment (see below) to attempt to reduce damage due to a collision.

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 Driving Support ECU Assembly determines if a collision is unavoidable based on object position, speed and track information. If the Driving Support ECU Assembly 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)
   • Brake booster with master cylinder (skid control ECU) (activates pre-collision brake assist system)
   • Brake booster with master cylinder (skid control ECU) (activates pre-collision brake)
2. When operating as a result of sudden braking:

   The brake booster with master cylinder (skid control ECU) uses brake pressure information and other data to determine if the driver has suddenly applied the brakes. If so, the brake booster with master cylinder (skid control ECU) sends a signal to the seat belt control ECU through CAN communication and the pre-collision seat belts operate.

1. The pre-collision seat belts operate depending on what the sensor detects, or whether sudden braking has occurred. The pre-collision seat belt motor retracts the seat belt to enhance pretensioner effectiveness.
2. Operating condition
   1. Refer to the sensor and sudden braking descriptions under "Outline of Pre-Collision System" (see above).

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 the rate of deceleration.
2. Operative condition
   1. Refer to the sensor description under "Outline of Pre-Collision System" (see above).
   2. When the driver depresses the brake pedal after the Driving Support ECU Assembly determines that a collision is high possibility:

      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 Driving Support ECU Assembly determines that a collision is unavoidable:

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

1. The pre-collision brake operation is performed depending on what the sensor detects. This system can be canceled by the pre-collision system cancel switch assembly.

   HINT: 

   While the pre-collision brake operation is canceled, the PCS indicator light on the combination meter turns on.

2. Operating condition
   1. Refer to the sensor description under "Outline of Pre-Collision System" (see above).
   2. When the driving support ECU assembly determines that a collision is unavoidable, the system performs brake control (pre-collision brake operation) to reduce the vehicle speed.

HINT: 

Each function will operate when all items marked (◦) are satisfied.

• *1: Operates when sudden braking or skidding is detected.
• *2: Does not operate in the following situations.
  • 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
• ◦: Main basis for operation
• -: Not main basis for operation

1. When the millimeter wave radar sensor detects an object in front of the vehicle under the conditions described below, the Driving Support ECU Assembly may determine that a collision is unavoidable, and activate the pre-collision system. This activation of the system is not abnormal.
   Fig 1: Identifying Cases Of Unnecessary Pre-Collision System Operation

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   HINT: 

   • The pre-collision system will not activate when approaching safety cones or other plastic objects as they cannot be detected by the pre-collision sensor.
   • 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.
   • Detection performance may deteriorate in the following conditions.
     • Vehicle height changes signifiicantly (front of vehicle inclined either upward or downward)
     • Millimeter wave radar sensor is misaligned (due to reinstallation or collision)

       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.