Vehicles made by Toyota, Honda, Kia, Hyundai, Mitsubishi and Fiat Chrysler from the 2010 through 2019 model years are included in the probe.
NHTSA investigators found more consumer complaints about airbag and brake problems.
Test results show the trucks had inflators that ruptured or recorded high internal pressure readings.
Automaker says it could save $1 billion and avoid recalling up to 6.8 million full-size 2007-2011 pickup trucks and SUVs.
Auto companies only halfway toward a Dec. 31 goal of 100% replacement of older and more dangerous inflators.
Government is wary of imposing costly mandates on the automotive industry.
Almost 10 million inflators with the highest risk of rupturing remained in use as of March 31.
NHTSA has found more than 2,700 complaints of exhaust odours in the passenger compartment.
Says propellant has not deteriorated in any of its inflators taken from vehicles in the field.
100 million inflators installed worldwide, could take years to get them off the road.
Inflator can separate from a plate, shooting out metal and other debris.
Tesla says sensors connected to the Model S’s autopilot system failed to detect the white truck as it turned into the path of the car.
Fiat Chrysler, Mitsubishi, Toyota and Volkswagen vehicles from the 2016 and 2017 model years.
Global recall of faulty airbag inflators likely to expand to more than 100 million.
NHTSA said it is satisfied the company has taken steps to prevent similar failures.