Mercedes Blind Spot Assist is a safety feature that warns the driver if another car is in the blind spot. This feature has been optional in many Mercedes-Benz models since early 2010. In this guide, we are going to take a look at some of the common problems with Mercedes blind spot assist and why you may get a warning message such as “Blind Spot Assist Inoperative” or “Blind Spot Assist Currently Unavailable. See Operator’s Manual”
Blind spot assist Inoperative Message
It is not uncommon to get blind spot assist has been deactivated warning on dashboard. Typically this happens during heavy rain. You may also get several other warnings on your dashboard including:
- Pre-Safe Functions Limited
- Active Lane Keep Assist Unavailable
- BAS and ESP lights on
The most common causes that trigger Blind Spot Assist Unavailable are:
- Heavy rain
- Inclement weather including snow and fog
- Extremely high temperatures
- Radar sensors in rear bumper dirty
- Driving too close to lane crash barriers or dividers
- Driving next to a truck for an extended period of time
- Interference from other equipment, or nearby transmissions (TV and radio stations)
In addition to the message on the instrument cluster, you may also notice the yellow triangle on the side mirror staying on. If you are expecting Blind Spot Assist problems, find a safe location where you can stop and restart the vehicle.
Troubleshooting Mercedes Blind Spot Assist
If you are driving in severely inclement weather avoid driving through water puddles. Wait for the rain to stop and restart the car and check if that did, in fact, reset the warning light. The system should reset on its own, and generally, there is no need to worry. Unless the blind spot system remains disabled the next day or this problem happens frequently.
If you are getting an error for blind spot assist inoperative every time it rains, you have a problem which you need to address. Blind spot system is not supposed to turn off every time it rains but unfrequent malfunction is common.
If the blind spot assist remains disabled, check fuses. If the fuse has not blown, check the follwoing:
Water in Radar Sensor
The most common problem is that the sensor can get damaged by water. If that’s the case, the blind spot assist sensors behind the rear bumper will need to be replaced. When the blind spot radar sensors in the rear bumper fail, the turn signals may also stop working. If you are getting a blind spot inoperative on your dashboard every time it rains, remove the radar sensors on the rear bumper and ensure they are properly sealed. Water may be entering the radar sensors triggering the message on the dashboard.
In some cases when the blind spot assist stops working the wiper blades may stop functioning as well. If you are experiencing these two problems check the fuse for the wiper blades. Most likely the fuse has blown. Once you replace the fuse, you should also gain access to the radar sensors in the rear bumper and inspect them. Make sure the radar sensors are completely sealed. When water makes it into these sensors it can blow the wiper fuse because these sensors are protected by the same circuit.
Dirt on Radar Sensor
Dirt on the radar sensors can prevent the blind spot assist from working properly. Remove the sensor and clean it if necessary.
Steering Angle Sensor
Another issue that makes the blind spot assist inoperative is the steering angle sensor which is mounted in the steering column. This sensor determines the position of the steering wheel. If it fails, the blind spot assist will not be able to get data and determine the position of the steering wheel.
If you are towing a trailer or another vehicle, you may also get “Blind Spot Assist Currently Unavailable. See Operator’s Manual”. The system should be back to normal operation once you remove the trailer. While you have a trailer attached do not rely on the blind spot assist system but always check the blind spots before you change lanes.
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How does Mercedes Blind Spot System Work?
First, we need to understand how the system works. Radar sensors installed on the rear bumper are used to detect vehicles in the blind spot areas. The radar sensors are behind the bumper. They are not the same as the parking assist (ultrasonic) round sensor you see. When a car is detected, the Blind Spot Assist will warn the driver via the triangle in the side mirror. If the Blind Spot system detects that you are getting too close to the other car it will apply the brakes on one side of the car to move you away from danger. Blind spot assist will only apply brakes if you are about to get into an accident such as when ignoring the warning or you try to change the lane when another car is next to you. If you are a careful driver hopefully you will never experience blind spot assist in action.
You should always check the blind spot when changing lanes. It is important to understand that Mercedes Blind Spot system works at speeds over 20 mph. Blind Spot Assist does not work if you are traveling at less than 20 mph.
Also keep in mind that, motorcycles may not be detected or if they are they may be discovered too late. Radar sensors installed on the front bumper and front grill, but those sensors are not used for Blind Spot system but Distronic only.
It also does not detect vehicles that are traveling significantly faster than you. Blind spot assist may not identify other cars if the lanes are very wide. That’s why the yellow warning light on your side mirror may stay on when driving slow. The yellow triangle on the side mirror should turn off once you speed is over 20 mph. Keep in mind that blind spot assist does not work when backing up. Blind spot assists monitor 10 feet behind the vehicle to the sides.
How to turn off /on blind spot assist
If you are going to tow a trailer or another vehicle you should turn off blind spot assist. To do so you can use the buttons on the steering wheel until you see the option for Blind Spot Assist. Enter this menu and turn it off using the OK button on the left side of the steering wheel.