General Motors Corp. plans to offer side curtain and dual-stage air bags in many of its cars, but won’t meet a deadline for introducing a system that stops passenger air bags from inflating if a child or child seat is in front of it.

GM said it had nearly perfected the suppression system but ran into problems in testing. The company wouldn’t say when the system could be available.

The side curtain air bags will appear first in 2001 Saturns, which should hit dealer lots late this year.

Unlike most side air bags that inflate from the side of the seat, the curtain air bags in the Saturns inflate from the roof, unrolling like a paper party horn within milliseconds of impact.

The system uses a sensor in the pillar between the doors that measures the force of any blow against the car. A second sensor between the driver and passenger seats determines whether the first sensor was detecting a crash or just getting whacked by a shopping cart.

GM engineers said the curtain design protects better against head injuries, especially for unbelted occupants. The federal government estimates that side air bags that protect the head could prevent about 600 deaths each year if they were installed in all cars.

The dual-stage air bags will appear as standard equipment on 2001 models of GM’s larger sedans — the Chevrolet Impala, Pontiac Bonneville, Oldsmobile Aurora and Buick LeSabre.

The system measures the force of a frontal crash and decides whether to set off the air bag’s full power or a second stage that’s about 70 percent as strong, said GM engineer Jim Khoury. He said tests had found the less powerful stage would be adequate in nearly all crashes while reducing air bag injuries up to 20 percent.

Air bags have been blamed for at least 145 deaths — mostly children and short women — in low-speed crashes that the victims otherwise should have survived, federal safety regulators say. However, they say, air bags have saved an estimated 4,600 lives in high-speed crashes.

The system GM had proposed that would automatically turn off passenger air bags isn’t ready for production because of testing problems, project engineer Mohan P. Thomas said.

That system uses a thin mat with 22 sensors sewn into the passenger seat to determine by weight whether the passenger is an adult, child or child seat and activate or deactivate the air bag.

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