BOSTON -- Just three days after Team 5 Investigates broke the news that there could be as many as 30 million potentially defective valve stems on cars nationwide, one of the largest Boston-area tire dealers joined the effort to warn drivers.

On Thursday Barry Steinberg, president of Direct Tire, recorded a public service announcement that will begin airing on radio stations next week, warning drivers of the potential hazard.

What To Look For | Photos: How To Spot Defects

Valve stems are a small, but critical part that is installed with every tire. It allows drivers to pump air into the tire. But if the valve stem becomes cracked air can escape, causing a flat tire or even a crash.

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Steinberg’s PSA warns drivers about the potential safety threat from cracked valve stems.

“You can ask people on the street, they’ve never heard of it. The car dealers aren’t acknowledging it so I figured I’d go on the air and let the public know there’s a potential problem,” Steinberg said.

The flawed valve stems could be on millions of vehicles, either bought new, or on replacement tires.

Tire safety expert Sean Kane warned, “We don’t know where they are. We don’t know how many cars have them.”

In May, the National Highway Transportation Safety Administration opened a federal investigation into problems with valve stems made at a Chinese plant in 2006.

As part of its investigation, NHTSA demanded a list of customers from Dill Air Controls Products, a company that distributes throughout the United States some of the valves that were manufactured at the Chinese plant.

But tracking the potentially defective parts will be difficult because Dill admits there is “is little traceability on these stems after they leave our facility.”

“They’re used all around the world in every single car and every single truck. But the public should check them,” said Steinberg. “It’s a safety issue.”

A cracked valve stem is suspected of causing an accident in Florida last November in which a 31-year-old man was killed. His family has filed a lawsuit.

No one knows what is causing the valve stems to crack. Several sources tell Team 5 Investigates the cracks may be the result of a mistake in the manufacturing process.