So first, thanks to the forum members for posting before about this as it saved me time and money, but here's my story.
Last year after a full week of heavy rain the notification for Blind Spot Inoperative popped up, quick check pointed at the sensors but since this is a secondary system i wasnt too worried about it and let it go. Then this year when the spring rains started my wife's ML350 decided to act up. She said it lost power and had a notification about the parking brake. When she got it to the side of the road it wouldnt go into gear. After several restarts she got it going. Next day same thing but at her work parking lot. Had it towed to my indy shop. They couldnt get it to do anything but the computers had a bunch of unrelated codes. A couple of days later it dies again but this time she grabbed some screen shots. This time it cycled through a whole slew of alerts like SRS, Seat belts, Pre-Safety disabled (does not have Distronic) etc. Engine would start fine but had to hold the start button in longer than normal. messages about gear selector and "take me to the dealer". My scan tool wouldnt connect and finally just went blank. Left it sit where it was in her work parking lot. Next day the sun came out and after about 6 hours, started it up and it went into gear just fine. No alerts except for the Blind Spot Inoperative. Drove it home. Pulled the rear sensors out, had to take the holder off as the sensors would not come out of the holders at all. I found the easiest way to get to the sensors was by taking off the wheels and pulling the wheel well liner. this seemed easier than pulling the rear bumper as it seems hard to get at the tail light screws etc. So once i had the sensors out it was easy to see how corroded they were. I bagged up the plugs and put it back together. The scan tool issue was that it blew the fuse for the ALDL connector. with that replaced I was able to connect and clear multiple codes. Car drives fine, even in the rain, expect of course the blind spot alert is still on. Ordered new sensors off of Ebay. I am hoping to get the sensors put in this week. My theory is this. These things generate a fairly high frequency wave (around 545Mhz-55mm is what I have read). I think when this high frequency bleeds through the corrosion which gets conductive when wet, it essentially creates "noise" on the ground that goes to every computer in the car. And with the CAN bus at 5 volts it doesnt take much noise to mess up the entire communications bus because the ground goes everywhere. Removing the modules clears things up (at leas in my case). I will update after I get the new modules installed, I'm expecting these to clear it all up and have the Blind Spot message gone as well.

 

Holy crap, I had the Blind Spot issue in my '13 GLK350, and now in my '15 ML350 (along with the Pre Safe warning). I never had time to dig into it, but this makes perfect sense. Many thanks for the disassembly tips, I'll definitely use 'em.

I wonder if it might be possible to clean and remove the corrosion to save parts replacement as long as they're not obviously irreparably damaged. Sometimes corrosion can be cleaned away successfully if connector p Also, I wonder about filling the connector with silicon brake grease to prevent water infiltration. Has anyone tried this?

I like the idea of using a bag to keep water out, but if moisture (any kind of humidity) gets into the connection we begin the slow corrosion process all over again. I've never successfully found a way to keep moisture out of a bag. Hmmmmm....I wonder if building wrap (I.e. trade name Tyvek) would prevent water infiltration while continually allowing any moisture to evaporate through it (that's what it's designed to do) that may possibly have entered. Could be sealed around the edges and onto the wire with the red tape used to seal this vapour barrier material.

Thoughts, anyone?

 

When I replaced my blind spot sensors with cheap wal mart knockoffs two years ago, I packed the socket with silicon plumber's grease and stuffed in the connector. Zero issues.
I've seen more than a few posts where someone pretty much coats the new sensor's plastic seams in silicone caulk. Not my cuppa joe but there's more than one solution to every problem. Some of them even work!

 

I've been through this as well. In my case it wasn't the actual connection. That is a fine example of Teutonic over-engineering complete with o-ring seal in a groove and strong clips. The problem is the completely exposed wire bundle at the "back" of the connector. The nickle connector pins were literally exposed to the elements, allowing salt water to wick up the pin and directly into the module. I considered using RTV but liquid electrical tape was a more elegant solution. Those connections are stupidly located - if you wanted to pick a worse spot its hard to imagine where that would be. They should be mounted inside the passenger cabin but what do I know? I'm just a humble wrench puller, not a educated German engineer. I read somewhere that there was another failure prone connection - it may have been on the AC compressor. It was low on the front of the engine, curbside. I goobered that one and the rear connections up 2 years ago and haven't had a whimper since. I also swapped out the rinky tink micro battery for a larger replacement which fit perfectly into the battery compartment that must have been used for earlier models. On my ML that battery box - roughly 9" x 5" - had a little bracket hung on it to contain the micro battery which would have been more suited to running a camera flash. Haven't regretted that swap either.

I was literally ready to give the car away 2-1/2 years ago when we left for Mexico. It had so many error messages and so many non-functioning systems that it simply wasn't driveable. We were gone for 3 months during which time the car sat in my heated shop with the ceiling fan lazily turning over top of it. When we got home I dreaded the ordeal ahead of me but when I hooked up the battery and started the car it was error free. After some serious thought I concluded that all the errors I had been seeing were simply OBD hallucinations and nothing has happened since to change my mind.

 

I only bagged the connectors while waiting for the parts to come in so they wouldnt be exposed. This was a little bit of a test to see if it would stay running when it rained which i can confirm did in fact work. The car did not "die" on the road like it had been doing.
as for the water getting in through the connector, i dont believe 100% that this is the infiltration point as one of my modules had no corrosion in that area. it was at the lowest part of the unit where installed. i suspect its more of a "breathing" effect from heating and cooling eventually sucking ins some moisture through the air, then when the corrosion gets bad enough it pushes the seal apart letting water in directly from the mist. That said, if a person pulled apart one that had not yet given the fault code and found some corrosion you MIGHT be able to clean it and reseal and hope from there, but in my case the boards are definitely damaged and for the cost of these Chinese ones i wasn't about to waste my time. Adding sealer around the edge might interfere with getting them in the holder as its a pretty tight fit as is. Liquid electrical tape might work to provide a seal around the connector and even a little of the wires where then enter the connector but that could also make them harder to get apart down the road. My connectors showed absolutely no sign of corrosion on them or the connector pins.

 

My experience with this same issue ended up being the harness that go across the bumper. The corrosion ruined the harness and so no connection was made with the sensor, I ended up mistakenly replacing the sensor before the harness so check for connectivity first.