M-Class (W166) Produced 2012-2015

Seatbelt tensions but doesn't let go ?

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Old 01-04-2012, 08:18 PM
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Seatbelt tensions but doesn't let go ?

Occasionally, maybe 1 out of 10 times, the driver's seatbelt will tighten up and then not loosen. Anyone else seen this?
Old 01-04-2012, 10:32 PM
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Originally Posted by TundraRoads
Occasionally, maybe 1 out of 10 times, the driver's seatbelt will tighten up and then not loosen. Anyone else seen this?
Never had that happen.
Old 01-05-2012, 01:57 PM
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Never had that happen to me.Sounds like you might be behind on your payments!

But seriously...that sounds like it's a potentially serious prob...I'd take it to the dealer ASAP.
Old 01-06-2012, 09:00 AM
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In to the dealer last night. Did it again to my wife on her way over there.
Old 01-06-2012, 10:11 AM
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Maybe the car really loves you guys.
Old 01-06-2012, 11:19 AM
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Originally Posted by TundraRoads
In to the dealer last night. Did it again to my wife on her way over there.
Murphy's Law says that they won't be able to recreate it and their computer shows no faults.If that's the case hopefully they'll just believe you and replace whatever parts might be involved.
Old 01-07-2012, 09:28 AM
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Of course, Murphy lives. Dealer found no faults and couldn't recreate (not surprising given that it only happens about 1 in 10 trips). When it happens again (I assume it will unless something with code scanning resets things and accidentally fixes it) we'll return it until they find the prob. Not a major issue when you're going slow, but it really concerns me when it happens on the highway.
Old 01-07-2012, 06:09 PM
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Originally Posted by TundraRoads
Of course, Murphy lives. Dealer found no faults and couldn't recreate (not surprising given that it only happens about 1 in 10 trips).
A seat belt is a vital safety device that,I'll wager,the NTSB (or another gov't agency) would take very seriously.If this was me I'd be on the phone with MB Headquarters in NJ demanding replacement of whatever parts (belts/pulleys/sensors) that are connected with that feature lest I personally make a call to DC and/or my Senator and Congresscritter.

But then I can get a bit hot-headed at times.

Last edited by listerone; 01-07-2012 at 06:12 PM.
Old 01-07-2012, 08:12 PM
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Maybe PreSafe was triggered?

From the owner's manual

"If the hazardous situation passes without resulting in an accident, PRE-SAFE®
slackens the belt pretensioning. All settings made by PRE-SAFE®can then be reversed.

If the seat belts are not released:

Move the backrest or seat back slightly, but only when the vehicle is stationary.
The belt pretensioning is reduced and the locking mechanism is released."
Old 01-07-2012, 08:44 PM
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Originally Posted by Wolfgang
Maybe PreSafe was triggered?

From the owner's manual

"If the hazardous situation passes without resulting in an accident, PRE-SAFE®
slackens the belt pretensioning. All settings made by PRE-SAFE®can then be reversed.

If the seat belts are not released:

Move the backrest or seat back slightly, but only when the vehicle is stationary. The belt pretensioning is reduced and the locking mechanism is released."
Sounds like the most logical explanation.
Old 01-07-2012, 08:47 PM
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Originally Posted by Wolfgang
Maybe PreSafe was triggered?

From the owner's manual

"If the hazardous situation passes without resulting in an accident, PRE-SAFE®
slackens the belt pretensioning. All settings made by PRE-SAFE®can then be reversed.

If the seat belts are not released:

Move the backrest or seat back slightly, but only when the vehicle is stationary.
The belt pretensioning is reduced and the locking mechanism is released."
Speaking from experience, the driver will know if PRE-SAFE is triggered. There are beeps from the IC, warning lights, etc. It's even crazier if the car has PRE-SAFE BRAKE - I nearly shat my pants!
Old 01-10-2012, 10:11 AM
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Good thought, but it doesn't appear to be pre-safe. My wife said that there were no warning lights or sounds accompanying it. While she was driving the belt just suddenly tensioned up and stayed that way. She had to unclip the belt.

Does anyone (MBTech?) know if it should have stored some kind of incident of this? I would assume any activation of pre-safe would store something. Any other reason than pre-safe it would tension? Anything in the drowsy monitor? Other?

Thanks,
Old 01-10-2012, 03:41 PM
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seat belt tensioning

Originally Posted by TundraRoads
Good thought, but it doesn't appear to be pre-safe. My wife said that there were no warning lights or sounds accompanying it. While she was driving the belt just suddenly tensioned up and stayed that way. She had to unclip the belt.

Does anyone (MBTech?) know if it should have stored some kind of incident of this? I would assume any activation of pre-safe would store something. Any other reason than pre-safe it would tension? Anything in the drowsy monitor? Other?

Thanks,
Found this on page 52 of the manual:

"The belt strap is tightened slightly when:
R
you engage the belt tongue in the belt
buckle and you then turn the SmartKey to
position
2 in the ignition lock.

R
the SmartKey is in position 2 in the ignition
lock and you then engage the belt tongue
in the buckle.
The seat-belt adjustment will apply a
retraction force if any slack is detected
between the occupant and the seat belt. Do
not hold on to the seat belt tightly while it is
adjusting. You can switch the seat-belt
adjustment on and off in the on-board

computer (
Y page 237)."
Old 01-10-2012, 08:03 PM
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Originally Posted by batuceper
Found this on page 52 of the manual: ...
Good find. I somehow missed that. Do you know exactly what that enables/disables?
Old 01-10-2012, 08:35 PM
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seat belt tensioning

Originally Posted by TundraRoads
Good find. I somehow missed that. Do you know exactly what that enables/disables?
Don't know, I have not had this problem.

But it reads to me like if the seat belt tensioning is enabled, it will detect loose belts and tension accordingly. I thought it may be worth a try?

I was just reading through the manual in the last couple of day to familiarize, after I got my car back.

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