SEAT BELT TENSIONER
DESCRIPTION
Seat belt tensioners supplement the dual front airbag system for all versions of this vehicle. The seat belt tensioners are integral to the front seat belt and retractor units (1), which are secured to the B-pillars on the right and left sides of the vehicle. The retractors are concealed beneath the molded plastic B-pillar trim. The seat belt tensioner consists primarily of a molded plastic tensioner housing (2), a tubular metal piston housing (3), a piston, a short rack gear, a set of pinion gears, a pyrotechnically activated gas generator (5), and a short pigtail wire (4).
All of these components are located on one side of the retractor spool on the outside of the retractor housing. The seat belt tensioners are controlled by the Airbag Control Module (ACM) (also known as the Occupant Restraint Controller/ORC) and are connected to the vehicle electrical system through dedicated take outs of the body wire harness by keyed and latching molded plastic connector insulators to ensure a secure connection.
The seat belt tensioners cannot be repaired and, if ineffective or damaged, the entire front seat belt and retractor unit must be replaced. The seat belt tensioners are not intended for reuse and must be replaced following any front airbag 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 8 - ELECTRICAL/RESTRAINTS/FRONT SEAT BELT AND RETRACTOR - REMOVAL).
OPERATION
The seat belt tensioners are deployed by a signal generated by the Airbag Control Module (ACM) (also known as the Occupant Restraint Controller/ORC) through the driver or 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 in one end of the tubular metal piston housing, which contains a piston and a small rack gear. As the gas expands, it pushes the piston and the rack gear through the tube. The rack gear engages a pinion gear that drives a gear set in the tensioner housing, which rotates the seat belt retractor spool causing the slack to be removed from the front seat belts.
Removing excess slack from the front seat belts not only keeps the occupants properly positioned for an airbag deployment following a frontal impact of the vehicle, but also helps to reduce injuries that the occupants of the front seat might experience in these situations as a result of a harmful contact with the steering wheel, steering column, instrument panel or windshield. Also, the seat belt retractor has a torsion bar mechanism that is designed to deform in order to control the loading being applied to the occupants by the seat belts 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. Proper diagnosis of the seat belt tensioner gas generator and squib circuits requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.