72 11... Checking automatic seat belt

General considerations when checking seat belts: 

The seat belts must be checked after an accident.

For the check, you should start by trying to get information on which seats in the vehicle involved in the accident were occupied. If this is not possible, check all the seat belts in the vehicle and replace them if necessary.

In the event of deformations on the vehicle, you must subject the components of the restraint system affected in this area such as e.g.

• Seat Belts
• Anchor fitting tensioner
• Seat belt height adjustment
• Belt buckle tensioner
• Triggering sensors
• etc.

to a function check and a visual inspection.

If you are in any doubt as to the unimpaired operability of restraint system components, these components must be replaced in the interests of safety! 

If a seat belt has to be replaced following an accident (e.g. in the event of a frontal and/or oblique collision with permanently deformed impact absorbers/deformation elements or cross-members), the complete seat belt must be replaced! The complete seat belt comprises:

• Upper seat belt
• Lower strap
• Anchor fitting tensioner
• Seat belt buckle (buckle tensioner)
• Seat belt height adjustment
• Mounting bolts of all components

The following must also be checked and if necessary replaced:

• seatbelt mounts on the vehicle body
• Seatbelt mounts on the seat
• seat rails.
• Seat structure (frame, etc.)

Alignment tests on the seat and the seat rails are not permitted! 

The following explanations and the CHECKLIST  for the automatic seat belt can provide help.

An unusable seat belt or a seat belt worn in a serious accident should be destroyed immediately after removal to guarantee that it can not be used again.

Checking automatic reel and seat belt strap: 

The automatic reel has two independent activation systems for seat-belt locking.

The first activation system locks the automatic reel when driving quickly around curves, driving in tight curves, on extreme inclinations (vehicle rolls over) and during sharp braking or crash.

To check, the seat backrest must be placed in the upright position and both hands held in a supporting position close to the steering wheel. The brakes are then operated with full intensity while driving on a dry roadway and at double walking speed.

The seat belt must lock.

The second activation system provides additional safety and is controlled by inertia mass.

If the reel locks when the seat belt strap is pulled out suddenly, this system is also OK.

In addition, the automatic electric reel (EMA) must eliminate belt slack.

Check whether an attempt was made to eliminate belt slack:

• Enter, close doors and latch seat belt buckle contact, left
• EMA eliminates belt slack

If belt slack was not eliminated, the procedure described below must be followed:

• Allow vehicle to assume complete sleep mode and repeat the functional check.
• All doors must be closed!
• EMA, left, must be installed and connected correctly.
• Work through all fault entries before the functional check is carried out again.

Replace defective or actuated automatic electric reels.

Automatic reel does not require servicing and must not be opened.

Precondition for complete, problem-free retraction of seat belt straps:

• the straps must not be twisted!
• the straps must not be damaged!

When placed to one side, the seat belt straps of the front seats must retract fully.

With the seat belt straps in the rear seat bench, a small remaining loop is acceptable due to increased friction between the strap and the rear seat bench cover if:

• this remaining loop is fully retracted when the seat belt strap is reguided.

Seat belt strap should only be cleaned with a lukewarm soap solution or a commercial mild detergent.

Seat belt strap must never be cleaned chemically or dyed.

The automatic reel and seat belt strap must be replaced in the event of:

1. creasing
2. unraveling
3. pinches
4. cracks and tears
5. traces of melting
6. traces of wear on coating of buckle tongue or on seat belt guide loop.

Checking lower strap (belt buckle tensioner): 

To fasten a seat belt, the buckle tongue should insert easily and with a loud click in the lock.

When the "Red button" is pressed, the buckle tongue must be ejected from the lock under spring pressure.

If the seat belt buckle cover is missing or damaged, the lower strap must be replaced.

Replace the triggered belt buckle tensioner including the complete seat belt with seat belt height adjustment and mounting bolts and check the

• seatbelt mounts on the vehicle body
• Seatbelt mounts on the seat
• seat rails.
• Seat structure

Criteria for a triggered mechanical belt buckle tensioner:

• very low position of seat belt buckle (comparisons with new part).

Criteria for a triggered pyrotechnical belt buckle tensioner:

• very low position of seat belt buckle (comparisons with new part).
• Airbag indicator light permanently lit: read out airbag system fault memory.

The belt buckle tensioners can be triggered under certain circumstances even when the seat is not occupied. If it is definite that the seat belt system was not used (seat was not occupied), there is no need to replace the

• upper strap
• Add-on parts (seat belt height adjustment, screws)
• seatbelt mounts on the vehicle body
• Seatbelt mounts on the seat
• seat rails.

after a check.

Checking end fitting pretensioner: 

Replace the triggered end fitting pretensioner including the complete seat belt with seat belt height adjustment, lower strap and mounting bolts and check the

• seatbelt mounts on the vehicle body
• Seatbelt mounts on the seat
• seat rails.
• Seat structure

Criteria for a triggered end fitting pretensioner:

• A triggered end fitting pretensioner can be recognized from the wrapped seat belt strap around the shaft.
• Airbag indicator light permanently lit: read out airbag system fault memory.