azipod

I had an unusual experience today driving the GS. I travelled across a bridge with metal grate flooring (I travel across this bridge everyday) at approx. 30-mph when all of a sudden, when the vehicle went across the metal grates, the seat-belt tensioner tightened up the entire belt pulled back forcefully suddenly and without any warning. The tensioner did not just lock me in place, but it actually pulled back the straps forcefully which glued me to the seat back for about 3 seconds before it let me go. It was quite forceful and scared me a bit. Almost felt like someone sitting in the back seat pulling on the belt as a joke. This has never happened before.

does anyone know if this is normal safety feature on the car?

LifeSimple

What year is it? Any codes or airbag lights?
Any aftermarket wiring?

azipod

2013. No codes or anything. Nothing wrong. All stock

john341

it is normal and is one of the safety feature. I believe it is called the seat belt pretensioner.. where you going down a hill and hard braking?

azipod

no. Just normal level driving at 30 mph constant but car transitioned from concrete pavement to metal grates on the bridge. Maybe the sensor got confused.

LifeSimple

That's exactly what I was going to say next, most likely it was the sensors prepping you up for a collision, at least you now know they work!

drgrant

I thought pretensioners are a one shot deal like an airbag- if they "fire" they're not going back to "normal" afterwards.

-Mike

bclexus

You better hope the pretensioner did not fire...because it isn't supposed to fire until a collision is actually already in the process of taking place. Also, when a seat belt pretensioner fires it needs to be replaced because it cannot be reused as a pretensioner again due to it having already been fired.

azipod

This is what I found from Lexus:

A pre-crash safety system containing a radar sensory system, occupant seat sensor, and an electric motor-pyrotechnic pretensioner system. During a pre-collision event, an electric motor in the pretensioners retracts the slack in the front seatbelts. When conditions stabilize the electric motor will reverse itself.

I guess my radar-system may have triggered a false alarm right when the vehicle was about to go on the metal grates on the bridge. This hasn't happened before and I travel on the bridge everyday. But perhaps its a one time hiccup. That's the most logical reason on why the pre-tensioners triggered.

As I understand it, Stage 1 is the electronic motor that pulls on the belt to retract any slack and to hold the body in place. Stage 2 is when the pyrotechnic blast occurs that will forcefully cause the seat-belt to remain "locked" during the collision. Nice to know the cool features that are on our cars!

bclexus

Did the driver's seat back adjust to the most upright position possible?

azipod

No, only the seat-belt tightened for a few seconds and then it let me escape.

bclexus

I thought the pre-crash safety system stood all seat backs into the most upright position before tightening the seat belts. I don't know - I just hope I never need the system's help!

azipod

Is that even possible? A crash occurs at an instant and I don't think a seat can adjust itself that quickly.

bclexus

Lexus' Pre-Collision System (if you have it) does. Look at about 3:15 in this video.

azipod

I do have PCS but the seats did not move on my GS. I don't know if the GS has it or not. Your video of the LS is pretty informative regardless.