Seatbelt holds passenger tight in seat all the time, 2002 tahoe

Question edited for clarity, full make model details.
Question moved from Spanish car maker Seat, (pronounced 'See-At') to make model category.

switch on passenger seat base - MBWorld.org Forums

https://mbworld.org > ... > SL-Class (R129)
Feb 2, 2006 - It's for when you put a baby/car seat in. It keeps the seat belt tensioner in one place after the seat belt is activated.
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Child Smart Seat for SL ' Mercedes-Benz Forum

https://www.benzworld.org > ... > R129 SL-Class
Jul 10, 2012 - Then there is a button to lock the seat belt of the passenger seat to secure the safety seat on it and deactivate the air bag. That lock button ...
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and lastly

https://www.benzworld.org/threads/child-smart-seat-for-sl.1662040/

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The reason is the belt mechanism is damaged and the belt needs to be replaced. What happens is the gears lock this usually only happens when the vehicle is in a collision or has a major and hard stop

TO get that screw out you need to use a tool that looks like a nail puller and you put it under the screw head to lift while you unscrew it. Once you get to the mechanism for the seatbelt, you should be able to free it because it will he able to have slack and the dogs will loosen up. Be mindful of airbags and seatbelt tensioners that are in that area though

The re-tractor is called an Inertia Reel. There on the side, remove the cover and there is a trigger release on most. If the spring is broken, you will need to replace the reel. Check at a local junk yard for the best price.

dc don

check to see if the electrical connection is connected at the base of the seatbelt (most newer cars have these and they lock the belts down forever in case of an accident) if this is connected then i would say you need to replace the belt

most common issue is the belt got twisted. You have to remove the cover and keep the lock from engauging...

It could have twisted on recoil and is now stuck. You'd have to remove the interior panel to view that.

On the really bad side, the seat belt pretensioner could have failed or fired and locked the belt in place. If that's the case, I'd have a mechanic replace it since you can trigger an air bag deployment replacing it yourself.

you may have to remove the bolt that holds the buckle to the floor. Try to push the belt into the retractor and see if it frees up.

I assume you are saying it is in the locked mode. It has an automatic lock mode for holding a child seat. When the belt is pulled all the way out, it goes into locking mode. You will hear it ratchet when the belt starts going back in.



Section 01-20A: Restraints, Active 1999 Taurus, Sable Workshop Manual
DESCRIPTION AND OPERATION Safety Belt, Lap/Shoulder The dual locking mode retractor on the shoulder belt portion of the combination lap/shoulder safety belt for the front seat passenger and rear seat outboard passengers operates in two ways:

1. In the vehicle sensitive (emergency locking) mode, the shoulder belt retractor will allow the occupant freedom of movement, locking tight only on hard braking, hard cornering or impacts of approximately 8 km/h (5 mph) or more. The front and rear outboard seat belt retractors can also be made to lock by pulling/jerking on the belt.
   

1. In the automatic locking mode, the shoulder belt retractor will be automatically locked and remain locked when the combination lap/shoulder safety belt is buckled and does not allow the occupant freedom of movement. This mode provides tight lap/shoulder belt fit on the occupant and on a child safety seat or infant carrier installation restraint.
   

1. When the combination lap/shoulder belt is unbuckled and allowed to retract completely, the retractor will switch to the vehicle sensitive (emergency) locking mode.
   

WARNING: REAR-FACING INFANT SEATS SHOULD NEVER BE PLACED IN THE FRONT SEATS.
The automatic locking mode must be used when installing a child safety seat on the front passenger seat and rear outboard seats where dual locking retractors are provided

They Are easy to replace, They mount to the floor with one large bolt. The nut  below is welded so if you can obtain a large enough socket ... You may als get one from a junk yard. 

The front seatblet retractor springs have weakened. Unfortunatly, there are no "user serviceable parts" on them. They would have to be replaced. How many miles is on it? If you have low mileage, the Toyota Customer Experience Center may provide you some assistance, as the belt replacements are quite expensive. I'd call the CEC and explain your dilemma. Here is the number: 1-800-331-4331