System common control unit with airbags (see chapter Onboard electrical equipment). The power supply to the mechanism drive is carried out in case of a frontal collision, causing an axial overload exceeding a certain certain value. Weaker impacts, as well as impacts from behind, do not trigger the system.
When the system is turned on, the gas ignites inside the cylindrical modules of the tensioners. In this case, the piston sharply moves forward, choosing the slack in the belt by retracting its stem. The explosive force in the cylinder is calibrated in such a way that, when the belt slack is selected, the body of the driver/passenger is firmly pressed against the seatback without excessive jerk. After a single operation, the tensioning mechanism becomes unusable and must be replaced.
To avoid the risk of injury from spontaneous operation of the tensioners during maintenance work on the vehicle, in particular the front seats, first disconnect the negative cable from the battery and de-energize the belt tensioning system. To disable the tensioners, remove the SRS fuse from its socket in the fuse/relay box. Work can only be started after at least five minutes after the fuse has been removed - this is the time required to discharge the reserve tanks in the SRS control unit.
When performing any service work on the front seats of the car, try to consider the following points:
Attention! After the seat belt pretensioner has been triggered, both pretensioners must be replaced together with the control unit!
Attention! Accidentally protected tensioning mechanism cannot be installed on the car and must be replaced even if there are no external signs of damage!
Attention! Never allow tensioner components to come into contact with any solvents!
Attention! A sharp blow to the front seat can cause the seat belt tensioner to deploy!
Attention! Do not overheat the seat belt tensioners!