Case Studies

Mercedes Active Blind Spot Assist – Care and Feeding – Problems, Repair, Service and Correction

What Is Mercedes Active Blind Spot Assist?
There’s a good reason that the obstructed area of vision over your shoulder is known as the “blind spot.” Both vehicles and other obstacles can hide in this area of your vision, creating the potential for a collision or other accident if unnoticed.

How Does It Work?
Active Blind Spot Assist
uses sensors and cameras to constantly monitor an area of up to 10 feet behind and immediately adjacent to your vehicle. If a vehicle is detected within the blind spot area, a red triangle warning indicator appears in the corresponding exterior side mirror. It’s important to remember that Active Blind Spot Assist is active at speeds above 18 MPH.

Should you fail to notice this visual warning in your mirror and signal for a lane change, the warning light will begin to flash, and an audible alert will sound. Finally, if you continue to attempt the lane change despite the warnings, Active Blind Spot Assist can (in certain models) apply corrective steering actions to keep you safely in your intended lane.

How Does It Fail?
The Mercedes Benz blind spot assist feature uses radar sensors to detect other objects or vehicles alongside and behind your car. The feature aims to alert drivers when it is and isn’t safe to change lanes by assisting them in detecting obstructions in blind spot areas. It is not uncommon to get a blind-spot assist that has been deactivated warning on the dashboard.

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.

Typically, this happens during heavy rain, and these problems resolve shortly when the environmental circumstances change. The most common causes that trigger resettable and temporaryBlind Spot Assist Unavailable” are:

  • Heavy rain
  • Inclement weather, including snow and fog
  • Extremely high temperatures
  • The radar sensors in the rear bumper are dirty
  • Driving too close to lane crash barriers or dividers
  • Driving next to a truck for an extended period

However, not all Blind Spot Assist problems are temporary or resolved on their own. On older vehicles, especially those operating in the climate of Maine and New England, where environmental weather conditions can be extreme, damage to the electronics of the Active Blind Spot Assist can actually occur. In the next paragraph, we’ll discuss the system’s weak points and common failures and what you can do to prevent or mitigate those problems.

Worse Case
Unfortunately, these sensors don’t live in the most hospitable of areas; they are found tucked under the rear bumpers, subject to water, snow, salt, and other debris from the road. It doesn’t take long, perhaps 3-5 years, before some of that water finds its way into the radar units (due in no small part to their location) under the bumpers and the electrical wiring harnesses. Water is vehicle electronics’ biggest enemy, and add to the corrosive effects of road salt, and you’ve got a rather toxic brew.

Internal Corrosion In the Mercedes Active Blind Spot Assist Modules

If water or corrosion is found in the sensor or the wiring harness, the best and safest course of action is to replace the blind spot assist sensors located behind the rear bumper. When the blind spot radar sensors in the rear bumper fail, the turn signals may also stop working, wipers can also be affected.

If you are getting a blind spot inoperative on your dashboard every time it rains, water may have entered the radar sensors, triggering the message on the dashboard. Sometimes, when the blind spot assist stops working, the wiper blades may also stop functioning. If you are experiencing these two problems, check the fuse for the wiper blades. Most likely, the fuse has blown. Water entering these sensors can blow the wiper fuse because the same circuit protects them; other problems relating to engine starting and running can also occur, which is why Active Blind Spot faults should be resolved as soon as possible.

At Atlantic Motorcar, for client satisfaction, due to the high failure rate of these modules and connectors from water, we take some additional steps to mitigate water entry into the modules and the wiring harness, using special weatherproof connectors, heat shrink tubing, and dielectric electronic grease. We recommend that these connections be checked yearly on A or B Maintenances to ensure they remain weather-tight. We do NOT recommend you place the modules inside plastic bags, as is sometimes mentioned. These bags invariably leak, fill with water, and cause condensation and water entry problems much quicker.

Proper Repair
The proper correction involves replacing one or both (depending on condition, most often replaced in pairs) rear blind spot assist sensor/radar units with OEM Mercedes parts. Replacement of the wiring harness with factory parts, sealing wire splices with special weather pack connectors, and heat shrink tubing to prevent water entry. Use special dielectric electronic grease to seal the multi-pin connectors on the radar units to the wiring harness seal.

Verification: Using Mercedes XENTRY Diagnostic Computer, erase fault codes stored, code and program for the new modules, teach in, and update software as needed for the vehicle. Test and verify the correction of faults and proper operation of new modules.

Our Goal For You and Your Car
Our goal is to save you money, not spend it. This is why each car we service gets a free Courtesy Maintenance Inspection during its first service visit. If additional work or service is needed, we’ll gladly advise you and offer a free estimate!

We aim to inform you about the minor problems before they become big. Right now, we have a number of customer cars with well over 200,000 miles and several approaching 300,000! And these cars are not just limping along – most look and drive pretty much the way they came out of the showroom.

Proper maintenance is an investment in the life of your vehicle.
Knowing, not just doing, but actually knowing and understanding the difference makes all the difference.

Be sure your car is properly loved.
Our professionals will attend to both your and your car’s needs.

Atlantic Motorcar…Extraordinary Service for Extraordinary Cars is just a phone call away: (207) 882-9969.


Accessibility Toolbar