Understanding the Collision Warning and Braking System

2014 Subaru Forester, EyeSight Camera.
2014 Subaru Forester, EyeSight Camera.

A key part of being able to diagnose a problem with Advanced Driver Assistance Systems (ADAS) is understanding how the system works. Knowing what is happening inside the system will help you properly diagnose why the system may be failing. This will prevent replacing parts that are not causing the system issue. Let’s take a look at the inner workings of a collision warning and collision braking system.

Collision warning systems will alert the driver to a possible collision. While collision braking systems will detect a possible collision, alert the driver, and apply the brakes. Both systems utilize and operate very similar to adaptive cruise control. Collision warning/braking systems primarily use cameras and sensors to detect objects in front of the vehicle. There are many variations in what is used to detect the distance. Some vehicles use an exposed radar in the front bumper, whereas some use a radar that is hidden behind the front bumper. There are even OEMs, such as Volkswagen or Cadillac, that utilize more than one radar behind the front bumper. Higher-end vehicles are beginning to use sensors, on the sides of the front bumper, to detect cross traffic at an intersection. Many systems utilize a forward-facing camera, near the review mirror, to help spot a possible collision. Some vehicles may also utilize dual cameras near the rearview mirror to control the collision warning/braking system.

Radar sensors works by sending radio waves that are reflected off of objects. The time it takes for the radio wave to return indicate how far away the object is, how big the object is, and what direction the object is traveling. Radar sensors are most effective when the object it is detecting is metal. So, the forward-facing camera is used to fill the gap so objects that are not metal can be detected. While most systems are designed to prevent a collision with another vehicle some, collision warning/braking systems can detect people, animals, and other objects as well.

The combination of the forward-facing camera and the radar work as a checks and balances system. If the radar detects an object, the radar will communicate with the camera to find out if the camera saw the same thing. If both detect the same thing, then a warning is given to the driver to stop the vehicle via a collision warning. If the driver does not apply the brakes in time, the vehicle will apply the brakes to mitigate or prevent the collision, if equipped with collision braking.

Normally the radar sensor has its own built-in module. This module makes all the calculations to send and receive signals. Forward-facing cameras may also have a module built in. These sensors and cameras detect if there is an object present and the distance to that object. The data from these modules is sent to other modules in the vehicle, such as the powertrain control module or ABS module, to slow the vehicle if a collision is imminent. There will generally be many modules that use data from the sensor and/or camera. Information from sensors, such as wheel speed, steering angle, and engine torque, can all contribute to the collision warning/braking system. If one of these parts is not functioning properly, it can cause the whole system to fail.

Understanding how the system functions can shorten diagnostic times. Knowing what part of the system to test will help prevent installing parts that don’t actually fix the problem.