Seat Belt Tensioner

Fig. 47 Seat Belt Tensioner:

SEAT BELT TENSIONER
Front outboard seating position seat belt tensioners supplement the driver and passenger airbags for all versions of this model. The seat belt tensioner is integral to the front outboard seat belt and retractor unit, which is secured to the inner B-pillar on the right and left sides of the vehicle. The retractor is concealed beneath the molded plastic inner B-pillar trim. The seat belt tensioner consists primarily of a die cast aluminum tensioner housing or chamber, a mechanical clutch unit, a tape-like metal strip, a pair of cutters, a pyrotechnically activated gas generator, and a short pigtail wire. All of these components are located on one side of the retractor spool on the outside of the retractor housing. The seat belt tensioner is controlled by the Airbag Control Module (ACM) and is connected to the vehicle electrical system through a dedicated take out of the body wire harness by a keyed and latching molded plastic connector insulator to ensure a secure connection.

The seat belt tensioner cannot be repaired and, if faulty or damaged, the entire outboard front seat belt and retractor unit must be replaced. If the front airbags have been deployed, the seat belt tensioners have also been deployed. The seat belt tensioner is not intended for reuse and must be replaced following a deployment. A locked retractor that will not allow the seat belt webbing to be retracted or extracted is a sure indication that the seat belt tensioner has been deployed and requires replacement. (Refer to RESTRAINTS/FRONT OUTBOARD SEAT BELT & RETRACTOR - REMOVAL).

The seat belt tensioners are deployed by a signal generated by the Airbag Control Module (ACM) through the driver and passenger seat belt tensioner line 1 and line 2 (or squib) circuits. When the ACM sends the proper electrical signal to the tensioners, the electrical energy generates enough heat to initiate a small pyrotechnic gas generator. The gas generator is installed at the top of the tensioner housing which contains a long metal tape that is routed through two chambers within the housing. Each end of the tape is wound around the outer sleeve of a mechanical clutch mechanism secured to one end of the torsion bar upon which the retractor spool is secured. As the gas expands, it is directed against the metal tape within the two chambers of the housing causing the tape to unwind from the clutch sleeve. As the clutch rotates it engages the torsion bar, which drives the seat belt retractor spool causing the slack to be removed from the seat belt.

Once a seat belt tensioning sequence has been completed, the forward momentum of the occupant results in deformation of the torsion bar. As the torsion bar deforms it allows the seat belt webbing to unwind from the retractor spool, which causes the metal tape to be wound back onto the clutch sleeve until it is pulled tight against two cutter blades within the housing, which immediately cut the metal tape.

Removing excess slack from the seat belt not only keeps the occupant properly positioned for an airbag deployment following a frontal impact of the vehicle, but also helps to reduce injuries that the occupant might experience in these situations as a result of a harmful contact with the steering wheel, steering column, instrument panel and/or windshield. The torsion bar is designed to deform in order to control the loading being applied to the occupant by the seat belt during a frontal impact, further reducing the potential for occupant injuries.

The ACM monitors the condition of the seat belt tensioners through circuit resistance, and will illuminate the airbag indicator in the ElectroMechanical Instrument Cluster (EMIC) and store a Diagnostic Trouble Code (DTC) for any fault that is detected. For proper diagnosis of the seat belt tensioners, a DRB III scan tool is required Refer to the appropriate diagnostic information.