Active Blind Spot Assist / Lane keeping Assist Inoperative

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New Member
Apr 28, 2023
Hi All, I have a W218 2015 CLS Shooting Brake showing the Active Blind Spot Assist / Lane keeping Assist Inoperative on the central dash board screen.
My assumption is that I have a faulty Blind Spot Assistant Radar Sensor...WHY
The active PARK assist (white arrow against the BLUE box) works on the left, but not of the drivers side.
The active lane assist and distance to car in front cruise control all work fine, as does the assisted steering.
My local garage did an analysis and suggested a communication issue with "RADAR 5".
I've looked under the rear bumper and can see a left, right and central Radar Sensor, black box with white on one side. I've removed Left and Right and they look good, no obvious cause for fault.
The front central Radar Sensor, behind the badge I believe is a long distance sensor and looks fine.
Following this train of thought, all left to check is Front Radar Sensor (left and right). What i can find is places online who will sell me a new one, however I can not see anywhere online showing diagram locating on the W218, where these are... On different models I can see these but am reluctant to start major strip down just to see if I can find them.
Any advice - possibly RADAR 5 means something to a guru, or maybe a parts diagram can confirm if indeed the W218 has a have front left and right...maybe accessible via the wheel arch. My intention would be to locate and inspect hoping to find an obvious fault.
After this the question would be is it a fit and replace part or do i need to re programme the new sensor. Other threads suggest once identifying the damaged part, finding one with similar part numbers (exactly the same) would allow plug and play... This is maybe a step to far but hoping my long explanation triggers interest from someone with previous knowledge on this. Sort of like problem solving on previous cars, however this one is really stumping me.
Any help, knowledge or support would be appreciated....
Did your local garage use STAR or a generic code reader? If the later you need to find a Mercedes independent with STAR. if the former you need to find a Mercedes independent who can use STAR properly.
Guessing and throwing parts at the problem gets expensive very quickly!
I have disassembled a faulty unit. They consist of a microwave part on one side
of a specialized PCB made up by a semi-ceramic material on one side and and "ordinary"
logics on the other side where the material is made up by fibre glass.
They are unrepairable since the schematic diagrams with parts lists are never made public as far as I know.

There has been problem with moisture ingress in theese units but from what I have heard, mostly affecting the rear ones.
I do not know the location of the front units. If you find the suspected one, make a careful inspection
of the cable harness. Check if the moisture sealant gaskets is OK. Check the connector for corrosion.
Thats about what anyone can do.

Where I live, a replacement module cost is about 800 Euros.

Reading this kind of makes me start to feel less annoyed about them missing from my CLS.
Thanks MB group for your input - Can anyone confirm that the W218 has front Left and Right radar sensor, used for the active park assit. On the back these are very visible, left, right and one facing backwards which I assume is a long distance radar.
I have a pdf copy of the Mercedes-Benz Driver Assistance Systems Technology Guide published in 2016 that details what components are present for which systems. In the section on Active Park Assist it mentions that it uses 10 x Ultrasonic sensors (those in the bumper surfaces), not the radar sensors used for Blind Spot Assist etc.

Happy to email you a copy, but with your limited posts you can't pm me your email address. Suggest you contact one of the Admins, point them to this thread and ask if they can forward me your email address.

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