jmow

2014 e 350 4matic with 27000 miles .had it to the dealer twice and currently letting them keep it overnight. problem is the driver side will take up the slack in the belt only half the time. dealer says no code showing and they dont know what the trouble is. could be the belt motor or more likely a problem in the latch. has anyone else had this trouble? i think i heard a slight grinding noise from the belt motor when it started acting up. any thoughts?

Oda112

Mine does that too sometimes. If I exit the car, lock it then come back, unlock it, get in, put the seat belt on before turning the car on, it will not tighten around me in some instances ( if the period between locking the car and getting back in it is no longer than 10 minutes). It always tightens if I put the seat belt on after starting the car. I don't know what the algorithm behind the operation of the pre tensioner is, but it is definitely not behaving in a constant manner. There are no error codes related to the pre tensioning system on my car either.

Johnny Rad

jmow

well i left the car with dealer while out of town. they came back with an answer that may be correct. they said you must start the car first and then fasten the seatbelt. i will test this out the next few days. funny how it always worked previously fastening the belt first??? thanks for the responses.

KEY08

rorywquin

I had an issue with the seatbelt on my SLK (also had the pretensioning - don't recall exactly what it was) but I just pulled it out as far as it would go and let it slowly rewind - think that over time the windings get a little messy. Solved the problem - might work for you.

jmow

is guess u have to follow the proper sequence to get it to snug u up. but for years it worked either way.

LILBENZ230

Digging up an old thread - do all 2014-2016 W212 cars do this auto snug thing? Or is it just on specific packaged cars? USDM.

DFWdude

Because this is a safety feature, I believe once each safety feature is implemented, then all cars have it. Someone please correct me if wrong.

LILBENZ230

Not sure with Mercedes - this could be a standard part of PRE-SAFE like it is on the W205 or it could be only in the PRE-SAFE Brake stuff you get with distronic. I was just curious as I am picking up a 2016 W212 this week and it does not have distronic.

DFWdude

Mine does not have Distronic, either, but it has all the pre-safe features.

LILBENZ230

Does it do the seatbelt snug thing?

DFWdude

It does indeed. Snug and release...

DFWdude

BTW, there is no order code for Pre-safe... I looked through my build sheet and could find no indication.

For me, that means it is standard, at least on all the facelift W212s.

kajtek1

What you guys are talking about?
Pre-tensioner acts only when you do panic brake- preparing the belts for potential accident.
I remember activating the feature twice in my life.

DFWdude

From Page 53 of the manual...

"The seat-belt adjustment is an integral part of
the PRE-SAFEŽ convenience function. This
function adjusts the driver's and front passenger
seat belt to the upper body of the occupants.
The belt strap is tightened slightly when:
- the belt tongue is engaged in the buckle and
- the ignition is switched on
The seat-belt adjustment will apply a certain
retraction force if any slack is detected
between the vehicle occupant and the seat
belt."

In short, when you first enter the vehicle, buckle up and start the ignition, the belt tightens over the upper body to "measure" the size of the seat occupant, and then releases. The belt will remember the setting and engage it (tighten and lock) in a dangerous situation.

It also notes (page 66) that "PRE-SAFEŽ PLUS is only available in vehicles
with the Driving Assistance package." So it may not be a standard feature afterall.

kajtek1

OK, so the thread has nothing to do with pre-tension.
Only the adjustment.
Pretension is standard for all MB for at least 20 years.