lar steel housing, a piston, a cable, a torsion bar, and
a small pyrotechnically activated gas generator. All of
these components are located on one side of the
retractor spool on the outside of the retractor housing
except for the torsion bar, which serves as the spin-
dle upon which the retractor spool rotates. The seat
belt tensioner is controlled by the Airbag Control
Module (ACM) and is connected to the vehicle elec-
trical system through a dedicated take out of the
vehicle wire harness by a keyed, snap-fit molded
plastic connector insulator to ensure a secure connec-
tion.
The seat belt tensioner cannot be repaired and, if
faulty or damaged, the entire 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 growling or grinding sound while
attempting to operate the seat belt retractor is a sure
indication that the seat belt tensioner has been
deployed and requires replacement. (Refer to 8 -
ELECTRICAL/RESTRAINTS/FRONT SEAT BELT &
RETRACTOR - REMOVAL).
OPERATION
The seat belt tensioners are deployed in conjunc-
tion with the airbags 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 (Fig. 39). When the ACM sends the
proper electrical signal to the tensioners, the electri-
cal energy generates enough heat to initiate a small
pyrotechnic gas generator. The gas generator is
installed so that it directs its expelled gas at the
underside of the piston in the cylinder. The piston is
connected to a cable that is wound around a pulley
on one end of the retractor spool. As the gas expands,
it propels the piston through the tube, which pulls
the cable and rotates the retractor spool to take up
slack in the seat belt webbing.
Once a seat belt tensioning sequence has been
completed, the forward momentum of the occupant
results in deformation of the torsion bar. 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 occupant
might otherwise experience in a frontal impact event
as a result of 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 loads being applied to the occu-
pant 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. The ACM will
illuminate the airbag indicator in the ElectroMe-
chanical Instrument Cluster (EMIC) and store a
Diagnostic Trouble Code (DTC) for any fault that is
detected. For proper diagnosis of the seat belt ten-
sioners, a DRBIIIt scan tool is required. Refer to the
appropriate diagnostic information.
Fig. 39 Seat Belt Tensioner Operation
1 - TUBE
2 - PISTON
3 - CABLE
4 - CYLINDER
8O - 32 RESTRAINTS VA
SEAT BELT TENSIONER (Continued)
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