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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 blind spot detection system.
The blind spot detection system uses the radar sensors in the rear of the vehicle. These sensors are normally behind the rear bumper on each side. However, there are some instances where the sensor is in a different location, such as in the tail light or in the quarter panel behind the bumper cover. On a select few vehicles, ultrasonic park assist sensors play double duty as blind spot sensors.
Radar sensors work 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.
There is normally an indicator on the side rear view mirrors that will light when there is an object in the blind spot. The indicator light can also be located on the door trim or on the A-pillar trim.
Generally, the radar sensors are set up as a master module and slave module. The slave module communicates to the master module, which communicates to other systems. If the slave module detects an object, the slave module will tell the master module that it sees an object. The master module, generally, will then talk to the door module to turn on the blind spot warning light.
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.
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Article validated in 2025