When a crash occurs, certain chemicals and devices work to inflate the airbag with air at a high rate of speed. According to investigations into these claims, the defects occur in the inflator and propellant devices. The chemicals used in this process were allegedly stored and handled incorrectly. This then caused them to react violently when crashes occurred.
In April of 2013, Takata announced that the parts were defective. However, a report from the New York Times suggests that the company knew about the defects as early as 2004. Furthermore, Takata may have even tried to destroy evidence proving so.