How often does your seat belt pre-tensioner activate?

[ericthered]

In my 2006 M35x the seatbelt pretensioners activate way too often.
I am getting used to it, but at first they almost got me into an accident by themselves - when you brake and are considering any maneuvering, having the tensioners suddenly yank you around is a huge distraction.

I drive a lot in traffic, but in my car these things just seem to be too twitchy.
(do not include track conditions)

[06M4.5]

Every time I drive aggressive.

[wingFeather]

Are you close to anther vehicle while applying the brakes suddenly? If so, give yourself more distance in traffic. The car thinks you're going to crash.

[ericthered]

Are you close to anther vehicle while applying the brakes suddenly? If so, give yourself more distance in traffic. The car thinks you're going to crash.

I'd rather use my brakes and not get too close to another car.

[Poirot]

So far, luckily, it has only happened once. Some jerk cut off the car in front of me which caused him to pull up short, which caused me to pull up short. Kinda scared me at first, almost like a death grip, but the car was looking out for me. I give her a pat every now and then to say thanks.


Poirot

[TDot]

When does the belts activate, when you simply slam on the brakes, or when you hit the brakes and a car is in front of you. Just curious from what wingFeather said because I didn't notice any sensors on the front of mine.

[wingFeather]

Both. If you have the laser cruise sensor, the belts will be more likely to kick in, since it would detect an imminent collision and boost the brake force. Without the sensor, you can still get the belts to tighten but you'd have to slam harder on the brakes. The cars with sensors will boost the brake force if it senses a collision scenario, which in turn activates the belts. I hope that makes sense... I'm tired.

[yosM45]

In my 2006 M35x the seatbelt pretensioners activate way too often.
I am getting used to it, but at first they almost got me into an accident by themselves - when you brake and are considering any maneuvering, having the tensioners suddenly yank you around is a huge distraction.

I drive a lot in traffic, but in my car these things just seem to be too twitchy.
(do not include track conditions)

With the OEM brakes...about twice a month.

With the g37 BBK and OEM pads, about once every two months.

With g37 BBK and Project Mu B-Force pads with zero brake fade, never.

There is a level located at the center column (b pillar) of your car. The ECU senses an unlevel yaw based based on the pitch of your car cause by agrresive braking, then reacts based on how long your brakes take to bring the car to complete stop (worse with fade).

So if you slam on your brakes and your car takes a nose dive, and take too long to decrease speed, it will engage thinking you're not going to able to stop in time. Many times it happens without brake fade if your stoping while traveling down hill.

[mexillis]

Very good info Yos. I've only had the them tighten on me twice, once with oem brakes and once with BBK. For me it takes some serious braking to activate and even when I drive hard on the backroads it never kicks in. OP are you someone who follows close and brakes hard everytime?

[Ilya]

Very good info Yos. I've only had the them tighten on me twice, once with oem brakes and once with BBK. For me it takes some serious braking to activate and even when I drive hard on the backroads it never kicks in. OP are you someone who follows close and brakes hard everytime?

This. I've had it happen 2 or 3 times in heavy traffic when something happens in front of me. On the backroads where I fly and do aggressive braking, never happened yet.

[The00Dustin]

Mine have come on 2 or 3 times in 3 years when I wouldn't have expected / needed them to, in those cases, it was going down a slight incline, which didn't even click as relevant until I read the end of the post by Yos.
They have also come on when I have tried to get them to by braking very hard, and when someone (cutting me off) or something (like a deer) has caused me to nearly be in an accident.

[ericthered]

This. I've had it happen 2 or 3 times in heavy traffic when something happens in front of me. On the backroads where I fly and do aggressive braking, never happened yet.

Then you've never come around a blind corner to see a wall of taillights.
It happens to me about once a year in the local mountains.

But this mostly happens in traffic at speed where (assuming no one is tailgating) I will abruptly brake to insure safe space in front of me. But this is not full braking, just quickly going from non-braking to fairly significant braking.

[ericthered]

So the tensioners activated again yesterday.

I was going 25-30 and the traffic light turned yellow.
I solidly hit the brake, pitching the car a bit.

Maybe two seconds later (after the tensioners activated) I let up with car going closer to 5 mph. No tire queal, and it didn't feel like a panic stop, just firm.
Of course the tensioners deactivated quickly, too.

I do apply the brakes firmly from the outset of braking causing a quicker change in pitch, but this seems way too touchy. Agreed?

[The00Dustin]

Doesn't typically seem too touchy to me. I would guess that you might have been on a slight decline as previously discussed, or you might have ICC and be a tailgater who thinks your following distance is fine. These are both guesses, though; it is also possible that the utility to activate your tensioner is too touchy due to previous damage or a defect.

[ericthered]

I was going 25-30 and the traffic light turned yellow.
I solidly hit the brake, pitching the car a bit.

Maybe two seconds later (after the tensioners activated) I let up with car going closer to 5 mph. No tire queal, and it didn't feel like a panic stop, just firm.

Doesn't typically seem too touchy to me. I would guess that you might have been on a slight decline as previously discussed, or you might have ICC and be a tailgater who thinks your following distance is fine.

At the light no one was in front of me or behind me.
And the intersection was level.

And come to think of it, I rent and drive lots of other cars, and never has a pre-tensioner activated on them.

[wingFeather]

And come to think of it, I rent and drive lots of other cars, and never has a pre-tensioner activated on them.

Not all cars have these. It is a pretty rare feature, actually.

If they are activating quite often, your sensors may be defective, or somehow the shocks are very worm - causing the vehicle to dip more than normal and trick the sensors.

[Allinf]

Having this seat belt retraction problem too. Seems to be too sensitive. It won't occur if I tap on brake pedal prior to the stop. I thought it might be that brakes needed to be bled, but after a flush and bleed, still have issue. Pads still have 50% left.

[ericthered]

I should have updated this thread some time ago.

My seatbelt pretensioner activation problem has entirely gone away, maybe it has happened once over the past 18 months in a situation where I expect pretensioners to engage.

I did not "fix" anything. At some point I upgraded my brakes with high-friction cryo-tempered rotors (mostly because front rotors would warp - I drive steep mountains every day), but I think the problem went away before that. Maybe it was the hard reset of the ECU?Just guessing, I don't know why it magically went away, at some point my wife and I noticed it just plain stopped happening.

On a related note, the M still does not stop as well as my old G50's stopped (e.g., '94 Q45t).