DETROIT -- The U.S. government's highway safety agency is investigating four automakers that have a potentially deadly type of Takata air bag inflator in their vehicles but haven't recalled them yet.

The National Highway Traffic Safety Administration says it is investigating Audi, Toyota, Honda and Mitsubishi in connection with a recent Takata recall involving 1.4 million inflators.

The inflators have a distinct and separate problem that can cause them to blow apart a metal canister and spew shrapnel.

The problem killed a driver in Australia in an older 3-Series BMW, which has already recalled more than 116,000 vehicles.

The problem is so dangerous that in some cases BMW has told drivers to park vehicles until repairs are made.