Around the late '80s Supplementary Restraint Systems (SRS) have been fitted as standard or optional items to some vehicles.  This system usually consists of a Driver's airbag abd front seat belt pre-tensioners but can also include (depending on the vehicle) passenger and side airbags.

SRS is designed to operate when the vehicle is in a head-on collision in excess of 30Km/h with a range of 30° to either left or right in respect to the longituse axis of the vehicle.

More recently there has been an introduction that provides additional protection if the vehicle is in a roll-over type accident.

If a fault is detected, the fault code is stored and the airbag remains out of operation until the code is cleared by the SRS diagnostic tool.