snarestud940

I have a 2015 S550 that has 66,000, and has become my everyday driver as of March 2021. Here in Connecticut, we had an ICE COLD day about 2.5 weeks ago, and it was about 0-5 degrees for a day. My car was parked at my office outside for about 6 hours, and when I turned it on, it started relatively ok. After letting it sit for about 15 minutes to get warm, and driving about 2 miles down the road, I got an audible sound, and the display read, "Active Lane Keep Assist Inoperative," "Active Blindspot Assist Inoperative," "Pre-safe Functions Inoperative," "Distronic Plus Inoperative." I pulled over, and turned the car on and off about 5 times and the messages did not go away.

I got home, let the car sit, and then turned it on a few hours later, and they were gone. Since that day, the same messages come up about once or twice a week, and usually go away after I turn the car off and on again. I get a few days when nothing happens, and then a day or two in a row where it happens once or twice.

I drive the car about 100-200 miles per week, and also had the main battery changed about 15 months ago. When the warnings don't show up, the features work completely fine! My guess is it could be the auxiliary battery? I don't know why this is changed when it was cold, but my guess is that cold day must have activated the problem?

Any thoughts? The wait time to get to a dealer is over 1 month!

carlosinseattle

All those faults could have been caused by low battery voltage, in the main or aux battery. They are stored and probably just need to be cleared. You might be able to purchase a cheap Harbor Freight code reader and clear the codes yourself. That way you know if it comes back there really is a problem.

snarestud940

thank you! There is no check engine light on, so would there actually be codes? Very ignorant when it comes to cars lol. Is this something straight forward?

Nice Ride

More than likely time to replace AUX battery in trunk.

snarestud940

thats what I'm thinking. Today it came on 3-4 times. I have the car parked for the night (8 hours), and I put a trickle charger on. Let's see what happens! The dealer can't get me in for a month, if it is the auxiliary battery. I don't know!

I'm also having some trouble from time to time with the keyless entry. In the cold, if the car is outside for a long time, the car needs to be unlocked by pressing the key fob, not by just putting my hand under the door handle.

2012 merc amg

Sounds like a Aux battery but makes you wonder why you didn't get the Aux Battery malfunction message on the middle screen. You could take off the panels on the right side of the trunk (passenger side) to expose the aux battery and take it to a Batteries plus store and have them put a tester on the aux battery and the main battery. If you didn't feel comfortable replacing the aux battery yourself you could buy one from Batteries plus and bring it to a independent Mercedes repair shop and have them replace it. Thats what I did recently. Dealer wanted 475 dollars to replace the aux battery and I got the battery from Batteries plus for 80 dollars and the independent shop installed it for me for 120 dollars. A 275 dollar savings. Make sure your plastic cover over the distronic sensor in the middle of the grill is clear of salt and road debris as that can make it so the adaptive cruise won't work and you get a error message.

vinflouen

Ice on sensors is a strong possibility.

VII

Yes obstructed camera and radar can cause this issue as well.

MBGuy2022

I get the Active Brake Assist and Active Blind Spot Assist warnings on mine a 2019 S560. After scanning for codes I found a bad Left Rear bumper radar sensor.

It also happened after a couple of Love Bugs splattered on my radar screen on the front grill.

snarestud940

Thanks Everyone! I made an appointment to for the dealer next Thursday March 2nd in the morning. Just weird that It only happens after the car sits. Today it happened during the first start up, then I restarted the car and it was fine all day. who knows.

Denis Osullivan

Funny you mentioned this sensor. I had the same sensor fail and dealer replaced via taking the rear bumper off. And then they told me the bracket was cracked that the sensor sits in. They ended using duck tape to secure it as the CPO wouldn’t cover a new bumper. It took three months to resolve/discover the solution.

Mitch Alsup

A couple of years ago, I was driving from Roswell to Austin in freezing rain. About an hour into the trip those same alarms went off. I put it up to the sensors being clogged with ice and not being able to get the radar or ultrasonic stuff out of the car and into free-space. When I got home, the front of the car was covered with about 1" of solid ice...... I can see how the radar and ultrasonics could not leave the body through the ports they are supposed to use. They come an go periodically, mainly associated with bad winter weather.

Joshua

I have exactly the same problem on exactly the same model and year - SClass W222 2019 S560.. Thank you for posting.
When you say "a bad left Rear Bumper radar sensor" do you mean the little disc parking sensors on the bumper of which there are 4 - one on each corner and 2 in the centre of the bumper ?

Denis Osullivan

Not that simple. It’s secured on the inside of the bumper and is an item that is about 6” x 5”. The bumper most likely will have to be removed

Joshua

Just thought I would add ....

If you can, before you commit to a new Aux battery, have one tested.

See my thread (search by my user name JOSHUA)
I recently had 3 warnings - lane keep assist, brake assist and blind spot assist were all inoperative and occurred at the same time.
I replaced my Aux Battery anyway ... This did not clear the problem warnings...

AFTER I had my new AUX battery installed I was curious and asked them to check the old battery. The result under loan was "good battery" but since it was 4 years old I went ahead and changed it anyway.

Hope this assist to narrowing down your problem

Joshua

You are right Dennis.
There is a very good Youtube video on removing an S Class Bumper. I shudder to think what the dealer may charge for labour if indeed the radar control module(s) happen to be the problem.