WASHINGTON - Federal safety officials are stepping up investigations of possibly faulty brake boosters in General Motors' trucks and of airbags that may spew dangerous fragments at drivers in Pontiac cars and minivans.
If the two investigations lead to safety recalls, they would require repairs to as many as 4.5 million vehicles, the National Highway Traffic Safety Administration said.
The agency expanded its investigation of airbags to include 1998-2000 Pontiac Grand Prix cars and 1998-2001 Montana minivans and upgraded it to the more intense level called engineering analysis.
The earlier preliminary evaluation was opened in March because of one reported incident involving a 1999 Grand Prix.
NHTSA, which is aware of only one incident, explained the rationale for a broader, deeper investigation: The agency, GM and its suppliers have been unable to determine why a 2-inch disk-shaped fragment of the aluminum inflator separated from the airbag assembly. It tore the airbag, broke off portions of the airbag cover and inflicted 'numerous injuries' on the driver. Similar airbags are in more than 600,000 vehicles.
In the brake case, NHTSA said it and GM have collected more than 200 complaints about vacuum boosters that failed, making full-sized 1997-2000 Chevrolet and GMC pickups and sport-utilities more difficult to stop.
The complaints include 25 reported crashes with eight injuries.
The agency has collected more than 500 other complaints about problems with brakes on the trucks, but officials said they contain insufficient information to determine whether they are related to the boosters.
GM has replaced 17,000 of the boosters in warranty repairs, NHTSA said. Some of the repair records indicate a rubber diaphragm in the boosters was torn or split, the agency added.
About 3.9 million of the trucks are in service.
NHTSA said it closed an investigation of rear-seat auxiliary heaters in 2001 Chevrolet Tahoe sport-utilities because it found insufficient evidence that a defect exists. The case had been opened after a fire in one truck.
The agency also said it opened one new defect investigation:
1998 SAAB 900
Problem: Passenger's frontal airbag deploys without a crash.
Complaints: Four, with three reported injuries.
Vehicle population: 9,000.