Forgetting to shut off a keyless vehicle has been a safety hazard for years, causing a growing number of carbon-monoxide deaths. But a proposed regulation to require warning signals and other precautions has languished in the face of opposition from the auto industry.

Now an effort is underway in Congress to force action on the issue, and at least one automaker has enlisted in the cause.

General Motors says it supports a bill introduced this week by Sen. Richard Blumenthal, D-Conn., that would direct the National Highway Traffic Safety Administration to adopt a rule addressing the danger. It would require automakers to include a feature that automatically shuts off an engine after a specified period of idling. The rule would apply to all new keyless vehicles, which make up more than half of new cars sold in the United States.

Because they don’t need to turn a physical key, drivers can forget to shut off a keyless vehicle. Some motorists, particularly older ones, have inadvertently left cars with the engine running in garages attached to homes, which have filled up with carbon monoxide and poisoned occupants, often while they slept.

The safety agency proposed a rule in 2011 that would have required automakers to install more beeps and alerts to draw attention to a running vehicle, an effort the industry opposed. Trade groups have said there is not enough data to support the rule. That proposal did not require an automatic shut-off feature.

The agency “has abysmally failed in protecting consumers,” said Blumenthal, a member of the Senate Committee on Commerce, Science and Transportation. “The reason for our legislation is to require the agency within months, not years, to make these devices standard.”

General Motors, which has installed an automatic shut-off feature in 31 of 39 keyless models from its Chevrolet, Buick, GMC and Cadillac brands, said it “supports the spirit” of the bill, designated the Park It Act. “This legislation reflects GM’s continued dedication to advancing automotive safety,” the company said in a statement. It would not say whether it planned to extend the safety features on its own to its entire fleet.

Ford, which has the automatic shut-off function on all its keyless models made after 2015, said it was reviewing the measure and would “work with the committee as it lays out its legislative agenda on vehicle safety.”

In May, The New York Times reported that 28 people had been killed and 45 injured by carbon-monoxide poisoning from keyless vehicles since 2006. At a hearing days later, Blumenthal sharply questioned the agency’s deputy administrator, Heidi King, about the issue and demanded that the agency adopt the rule it proposed in 2011.

Since then, five more fatalities have been identified by The Times, including three in December and January.

Across manufacturers, there is no consistency in the safeguards to protect motorists against the carbon-monoxide hazard. Some carmakers have gradually introduced an automatic shut-off feature, but others use only sounds or visual alerts to warn motorists of a running engine.

Asked if it would follow General Motors in backing the Blumenthal bill, Hyundai also said it was studying the bill. Toyota, Mazda and Volkswagen referred to a statement by an industry group, the Alliance of Automobile Manufacturers, which said that “current keyless ignition system designs generally follow the recommended practices” of the Society of Automotive Engineers, a car standards body.

Toyota vehicles, for example, beep externally three times, and once inside, to inform drivers getting out of a vehicle that the motor is still running, a set of alerts that meets the voluntary standards. Toyota does not have an automatic shut-off feature. Its vehicles, including Lexus models, have figured in almost half of the fatal incidents identified by The Times.

Fiat Chrysler, which began introducing an automatic shut-off in its 2018 Chrysler Pacifica hybrid minivan, did not respond to a request for comment on the Blumenthal bill.

The legislation also aims to address the danger of rollaway vehicles, a hazard heightened by keyless ignitions because a driver can leave with the key fob without putting the car into park, regardless of whether the engine is running. The legislation would require carmakers to install technology that prevents a car from moving if the driver’s door is opened, the driver’s seat buckle is unfastened, and a brake is not engaged.

According to the agency, 142 people were killed by rollaways in 2015, the most recent year for which data is available. It is not clear how many of the vehicles were keyless.

In January, the highway safety agency said that it continued to review public comments on its 2011 proposal, and that it was “evaluating a range of options to determine the best path forward to optimize safety.” It also pointed to a safety video it released in 2016 to highlight the carbon-monoxide and rollaway hazards of keyless vehicles.

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