Description of Function of Airbag with Seat Belt Tensioner C. - Seat Belt Tensioner Unit - ra9100140c600x(0600)

Model 140 

General 

The risk of injury to the head and chest in the case of serious frontal collisions is further reduced by means of the driver's/front passenger's airbag unit in combination with the three-point seat belt and the energy-absorbing covers on the driver's and/or front passenger's side.

The driver's and front passenger's airbag units are marked "SRS Airbag". The warning light is marked SRS (Supplemental Restraint System).

Both systems are activated electrically by means of a control device in the event of a moderate to serious frontal collision. Our present knowledge indicates that, if undamaged, the entire airbag and seat belt tensioner restraint system should have a fully operational life of at least ten years. In contrast to the three-point seat belt, which only offers protection when worn, the vehicle occupant cannot influence the protection afforded by the airbag and seat belt tensioner system in any way. A properly worn three-point seat belt and the driver's airbag and front passenger's seat belt tensioner system are essential if this increased protection is to be fully effective.

The airbag and seat belt tensioner restraint system offers increased protection in the event of a frontal collision only. No protection at all is offered to a vehicle occupant not wearing a three-point seat belt in the event of a side collision, rear collision or roll-over.

Fig 1: Identifying Airbag Function For Seat Belt Tensioner

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's Airbag 

Fig 2: Identifying Driver's Airbag Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's/Front Passenger's Airbag 

Fig 3: Identifying Driver's/Front Passenger's Airbag Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's Airbag USA Version 

Fig 4: Identifying Driver's Airbag (USA Version) Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's/Front Passenger's Airbag USA Version 

Fig 5: Identifying Driver's/Front Passenger's Airbag (USA Version) Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Arrangement of Components 

Driver's Airbag with Seat Belt Tensioners 

Fig 6: Components Arrangement - Driver's Airbag With Seat Belt Tensioners

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Arrangement of Components 

Driver's/Front Passenger's Airbag with Seat Belt Tensioners 

Fig 7: Components Arrangement - Driver's/Front Passenger's Airbag With Seat Belt Tensioners

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

NOTE: In the case of vehicles in the version the components listed are located in the same position.

Stick-on Label for Replacement Date of the Driver's Airbag Unit 

The stick-on label with the replacement date of the airbag unit is located on the left-hand center pillar below the belt fastener.

Fig 8: Identifying Label For Replacement Date Of Driver's Airbag Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Stick-on Label for Replacement Date of the Driver's/Front Passenger's Airbag Unit 

On the left-hand center pillar below the belt fastener there is a stick-on label with the replacement date of the driver's and front passenger's airbag unit. The replacement date refers to the entire driver's and front passenger's airbag unit in each case. The operating life is at least ten years.

Fig 9: Identifying Label For Replacement Date Of Driver's/Front Passenger's Airbag Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driving with the Airbag and Belt Tensioner Restraint System 

When the ignition key is in position "1", the red warning light with the "SRS" symbol in the instrument cluster should light up.

The warning light shows that the airbag and seat belt restraint system is in proper working order. In ignition key position "1" it should light up for approx. 4 secs and then go out again. If it fails to light up or to go out after the stated time, there is a fault in the system. The error time is recorded by the control device (N2/2) and can be read out afterwards.

Fig 10: Locating SRS Warning Light

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Should an error be indicated in the above-mentioned way, the entire system must be checked as exhaustively as possible by trained staff via impulse output.

The operation of the standard-fitted driver's and front passenger's seat belts is not impaired by such a fault.

The complete airbag and seat tensioner restraint system consists of the following components:

1. Driver's airbag unit
2. Front passenger's airbag unit
3. Seat belt tensioner unit
4. Control device
5. Warning light
6. Energy-absorbing cover under dashboard (driver's and front passenger's side)

C. Seat Belt Tensioner Unit 

Cable Tensioner - Design 

Fig 11: Identifying Seat Belt Tensioner Unit Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function 

The complete unit is installed in the left and right-hand center pillar and electrically connected via a double plug.

Before the seat belt tensioner unit is installed, it is automatically electrically short-circuited with a short-circuiting bridge. The short-circuiting bridge is automatically opened when the connector plug is inserted.

When an electrical impulse is sent from the airbag and/or from the seat belt tensioner control device to the ignition capsules (R12/1, R12/2), burn-up gas is produced under high pressure. This fuel gas is fed via a T-piece to the piston (2), which is then accelerated upwards in the pipe (3). The cable wheel is set in motion via the cable (8) located in between and is power-linked to the reel shaft via the coupler.

The reel shaft is wound back, thus eliminating the seat belt slack and film reel effect. The seat belt then sits tight on the person in question and provides increased protection.

The forces used in the seat belt tensioner have been specially calibrated so that the belt does not pull the occupant back into the seat.

Fig 12: Identifying Seat Belt Tensioner Unit (Cable Tensioner Function)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

There is an observation window (20) on the seat belt tensioner housing, through which a notch can be seen. Seat belt tensioners where no notch can be seen have been triggered and must be replaced.

Fig 13: Identifying Ignition Capsules

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.