Understanding the Lane Departure Warning/Lane Keep Assist Systems

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 lane departure warning/lane keep assist (LDW/LKA) systems.

LDW/LKA systems utilize a forward-facing camera, located near the interior rearview mirror. Depending on the OEM, the vehicle may be equipped with or more cameras.

On vehicles equipped with a LDW system, the forward-facing camera looks ahead of the vehicle, and finds the lane marking lines on the road. If the camera sees that the vehicle is getting close to crossing over the lane marking line, a warning is given to the driver. The warnings can vary from a message or symbol on the instrument cluster to a haptic warning, such as the seat or steering wheel vibrating to a chime or sound, or any combination of these.

The next step, if the vehicle is equipped with a LKA system, is if the driver continues to travel over the lane marking lines, the camera tells another system to move the vehicle back into the center of the lane. The other system may be electronic power steering or ABS module. In systems using the ABS module, the brakes can be applied lightly to one side of the vehicle to make the vehicle move over.

Other things to know about these systems are that using the turn signal will disable the system because the vehicle realizes the driver intends to leave the lane. Also, most vehicles will either turn off the LDW/LKA system or tell the driver to pull over if the driver continues to ignore the warnings.

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