hornethandler

All Active Multicontour Seat functions (Lumbar, Massage and Side Bolsters) stopped working in the middle of a two hour drive. Seat position controls and seat heating worked normally.

Both batteries checked fully charged when I got home, so I don’t think it went into power saving mode to preserve battery life.

I briefly shut the car off and on, and then did a “Seat Reset” via the center console display to see if that would help, but no joy.

Once I got home and let the car set for an hour or so, everything started working again.

Has anyone experienced this? Any ideas?

Thanks!

crconsulting

Software glitch? Intermittent electrical issues are always hard to track...
Hopefully it won't happen again, but at least if it does, it may be easier to track.
It probably triggered a code in XENTRY. But without a way of reading the chassis code that wont help...
Besides checking fuses and resistance/load testing main battery. There's a control module in the back that may be malfunctioning. That would be my first suspect, but may also be a bad ground.

Were both seats affected?

Good Luck

hornethandler

Thanks for getting back.

Yes, both seats were affected.
Where exactly is the control module located? I'd like to reseat that connector.

According to the fuse chart that came with the vehicle, there are 6 seat related fuses:
4 in the panel behind the passenger seat, and 2 in the panel in the drivers left foot well.
The chart does not specify which circuits the fuses protect.

I should have mentioned this in the first post:
After the car sat for an hour or so, I reseated--the original fuse was good-- one of the two 30 amp fuses in the panel behind the passenger seat. After that, everything worked again. The fuse in question, and the other 3 seat fuses in that panel, were dry and free from any corrosion.

The other 2 seat fuses, located in the drivers left foot well panel, were too difficult to access so I didn’t check them.

A MB Rep. and personal friend said it’s not unheard of for electrical glitches to reset after shutting down the vehicle and/or opening and closing the driver's door.

I just checked again today and everything is still working.

Rethinking my decision to not get an extended warranty.

crconsulting

Then it's most likely not module issue, as they are independent, one for each seat.

see attached pdf's

Pulling fuses could have reset the system. As you're obviously aware, sometimes even pulling fuses and reseating connecters is all it takes to fix an issue. Mild internal connector corrosion can be hard to spot. Problem with electrical issues, is you have to be patient and make only one change at a time. If you change 10 things, and the problem, goes away, it will be difficult to diagnose what the actual cause was.

Haha, if you work on planes you know, the software drives the hardware. Modern cars can have glitches, just like the software on a PC. Sometimes it needs a good reboot. I'm sure the car stored a code. XENTRY is helpful in giving clues to aid in isolating the potential culprit. Most cars I scan have a few "false" codes stored. Once reset, they don't come back.

hornethandler

Once again you’ve come through!
Thanks for all the docs; I’ll give them a good look over.

I totally get the “change one thing at a time”. It was only after I reseated fuse #63 that everything came back to life. After that I reseated the other seat fuses as well for good measure.

Is there a document that shows the circuits individual fuses protect? It would be interesting to see what circuit is on the 30 amp fuse #63.

crconsulting

I’m traveling for a couple of days so away from my shop. But in case you don’t have them, there’s a bunch of pdf’s in this thread which may also be helpful:

https://mbworld.org/forums/sl-class-...ml#post8237257

hornethandler

Thank you!

hornethandler

Crconsulting, thanks for your help and for all the docs! The fuse numbers are not labeled on the actual fuse block or in the manual, so the docs. were very helpful.

Turns out the fuse (#63) I reseated was for the Airscarf Control Unit. So, reseating that fuse was not the reason the Active Multicontor Seat functions started working again.

Still at a loss as to why the seat functions stopped while driving, and then started working again after the car was shut down for an hour or so.
I’ll keep a close watch on the system and report back with anything conclusive.

hornethandler

Well, it happened again today. All Active Multicontour Seat functions--on both seats--stopped working near the end of a 1.5 hour drive in the country.
However, this time everything started working again immediately after shutting down and restarting the vehicle.
I'm still under OEM warranty so will try to book an appointment and have the codes read.
Once I get more info I'll post an update.

crconsulting

Intermittent electrical is always a pain to track. My experience is, if it works when you first turn on, and for a good while after that, then shuts down. It tends to be the in the modules somewhere vs. wiring. But as in all things electrical, not always . Usually solder or some passive component in the modules (just like any computer component) fails after some it gets some heat in it.

I would hook it up to XENTRY and get any clues stored there. At least it will give you a starting point....

Good Luck

Tommyboy928

do you have leak sound engine off, and try switch massage on ? often the hoses leak, they seperate where the hoses fitted to where they glued , we fixed some seats , massage will turn of to save the pump when detect leak .

hornethandler

I’m not hearing leaking noises during massage with the engine on or off.
When the seats are working you can hear the pump and feel the seats respond.
Massage was not turned on when the system stopped working. I was only using the active side bolster at the time; however, all Multicontor seat functions stopped working.

Observations:
The seat adjustment (massage on/off, lumbar and side bolster) changes are correctly indicated on the Command Control Unit (display); however, neither seat responds and the pump cannot be heard.
Also, seat position (lumbar and side bolster) indications go to “0”, and the massage “On” indication switches to “Off”, when the control (Command Controller switch) is released.
From what I can determine from the docs. provided by crconsulting, the only common component--besides the Command Control Unit--to both seats is the seat pump.

It would be interesting to see if the pump is receiving signals. I assume it would be pretty easy to check.

Does anyone know where the Active multicontour seat pneumatic pump (code # M40/1) is located?

crconsulting

It's in the trunk. This may help:
https://www.mercedesbenz.parts/v-201...-and-connector

There are also some components to that system in the seat itself.

hornethandler

Thanks crconsulting!
Is that the same pump that operates the soft close doors?

crconsulting

Soft close doors on R231 are electrical.

hornethandler

Thanks!

hornethandler

Yes, I saw them in the docs. you provided. Since it was both seats I figured it was most likely something common to them.
I'll take a look at the pump to see if there's any way to monitor the electrical signals to the pump to determine if it's the pump, or the command signals to it.

crconsulting

Agree.

Good Luck!

hornethandler

Thanks!
I'll get back once I learn something.

Wolfman

While all this is interesting I wonder why you bother if the car has factory warranty to cover this.

hornethandler

My warranty ends late Sep. 2023 and I have an appointment booked for next month--that was the earliest available--but because of the intermittent nature of the snag, it's not likely MB will be able to reproduce it.
The snag has only happened on two separate occasions, and only after over an hour of driving time, so I'm preparing for what will most likely happen:
MB will claim "no fault found" and I will end up trying to fix it myself.

There's another reason, though... there's a lot of great folks and knowledge on this forum, and I just enjoy sorting out problems.

hornethandler

For anyone who’s following, here’s an update on the snag.

In an effort to duplicate the snag, I electrically disconnected the seat pump in the trunk. It has one 4 pin connector with two large, and two small diameter wires.
According to the Electrical Function Schematic, I’m guessing the two large wires power the pump motor, and the two smaller wires transmit/receive the status/request signals to control pump operation.

Observations
The symptoms with the connector disconnected are exactly the same as when the snag occurs:
“The seat adjustment (massage on/off, lumbar and side bolster) changes are correctly indicated on the Command Control Unit (display); however, neither seat responds and the pump cannot be heard.
Also, seat position (lumbar and side bolster) indications go to “0”, and the massage “On” indication switches to “Off”, when the control (Command Controller switch) is released.”

So, one way to duplicate this exact snag is to disable the status/request signal at the seat pump in the trunk. I’m only guessing that it’s the status/request signal, but it could be that the whole pump assembly was electrically disconnected.

For now, since that connector has been reseated several times, I’ll drive the car and see how things go. Hopefully it was a little corrosion on the connector, I have my doubts, but hopefully.

crconsulting

I think as you surmised in the post #17, since it was both seats, it was most likely something common to them.
Exactly...
I've repaired several electrical "problems" this way. But success rate is low.
You should note the mileage and date in which you did that. When the tech scans the car with XENTRY, it will probably have stored a code for this event. You don't want an inexperienced tech to come back with the quick diagnosis of replacing the the pump if it's not the issue. Hopefully that information can be communicated to him directly, as things are often "lost in translation" when going thru the service writers.

Good Luck.

hornethandler

Thanks for the advice.
I will note the date and Km I disconnected the pump and advise the service dept. I’m hoping to talk to the tech one-on-one to give them details of the snag, and what I did.
In my experience it’s a delicate line as you don’t want to come across as telling them their business. Technicians are much like artists... they're sometimes very protective of their craft.

hornethandler

Update for those following:

The Mercedes tech identified a very slow leak in the drivers’ side Backrest Sides (inflatable bolsters). The leak is in the inflatable bolster itself and not in the air line.
Mercedes uses a pressure/vacuum tester--similar to an aircraft pitot static tester--to pressurize and to pull a vacuum on the inflatable seat components to check for leaks.
The tech explained that the reason the slow leak caused an intermittent failure in all Active Multicontour Seat functions in both seats, is because when a leak is detected, the Seat Pump Motor shuts down to protect itself from overheating. The pump then resets after a period of time.

The inflatable bolsters come as a set, i.e., each seat has two, and cost around $300.00 CDN; I have an appointment on 26 Jun. to have them installed.

I’m still under warranty so will let them do the job; however, according to the tech, it’s not too difficult a job to R&R the inflatable bolsters. If that’s the case, I’m thinking a simple bicycle tire repair patch will do the job if it ever happens again.

Hopefully all goes well and I'll report back to confirm the fix.