When independent mechanic Joe Marconi replaced a faulty windshield-wiper switch last summer on a 2004 Saab—a minor type of repair often done at his shop—the car wouldn't start.

Mr. Marconi, who owns Osceola Garage in Baldwin Place, N.Y., discovered the switch needed to be "initialized," something only a Saab dealership can do. Initializing is a problem that has been happening more and more often, says the 55-year-old mechanic.

"The entire car basically has to be reprogrammed to accept the new part," he says. In the end, he was forced to pass the vehicle, and his customer, on to the dealer.

Many garage owners hope the new small-business-friendly tone in Washington, including sweeping regulatory reviews unveiled last month, will re-energize the Right to Repair Act, a bill they say levels the playing field with auto dealerships.

The bill, which in various forms has languished in Congress for nearly a decade, requires auto makers like Ford Motor Co., General Motors Co. and Toyota Motor Corp., to supply smaller repair shops with the same onboard-computer data they give to their affiliated dealerships. Technology in newer vehicles controls everything from the steering wheel to the fuel delivery system, brakes, air bags, tire pressure and more.

Supporters, including a range of auto-service-trade associations, consumer groups and small-business advocates, say the move will boost competition in the auto-repair market, forcing dealerships to lower prices.

Auto makers, who fiercely oppose the bill, say they need to protect trade secrets from cheap generic parts makers. The car makers say mechanics already have access to what they need to get vehicles back on the road.

Yet there appears to be some grass-roots support for the bill. A survey in November by AutoMD.com, an auto-repair-information website, found 83% of 2,800 car owners polled said they favored right-to-repair legislation. Supporters have shown up on Capitol Hill in jumpsuits and overalls to rally lawmakers to pass the measure.

Initially introduced by Rep. Joe Barton (R., Texas) just before the Sept. 11, 2001, terrorist attacks, the bill was buried under a wave of national-security legislation. It has since been reintroduced in every federal legislative session, only to get bogged down amid strong lobbying by auto makers and dealers. The latest version was sponsored last year in the Senate by Sens. Barbara Boxer (D., Calif.) and Sam Brownback (R., Kan.), while a bill put forward two years earlier by Reps. Edolphus Towns (D., N.Y.), Anna Eshoo (D., Calif.) and George Miller (D., Calif.) had more than 60 co-sponsors, including high-ranking members from both parties. Both Sen. Boxer and Rep. Towns expect to reintroduce the bill as early as possible in the new session, with concessions aimed at easing auto makers' intellectual-property concerns, their spokespeople say.

But supporters say the bill may stand a better chance in states such as New York, New Jersey, Massachusetts, Connecticut—and in Kansas, where Mr. Brownback is now governor.

Last July, the bill passed the Massachusetts state senate only to collapse when the House closed its regular session—the closest its come anywhere to being enacted—after debate on a casino-licensing bill put all other issues on hold. State lawmakers there also expect to reintroduce the bill later this year.

"We think the momentum now is at the state level," says Aaron Lowe, vice president of regulatory and government affairs at the Automotive Aftermarket Industry Association, a Bethesda, Md.-based trade group that has lobbied for the bill since 2001. It estimates that repairs cost up to 34% more at dealerships than small repair shops, or an extra $11.7 billion spent by drivers on their cars every year. "Once it's adopted in one state, we expect it'll spread to others pretty quickly," he says.

Auto makers aren't going to let that happen without a fight. "The problem is they want full access to all the computer information, not just the repair codes but also the design and manufacturing codes. And that's where intellectual property kicks in," says Gloria Bergquist, a spokesperson for the Alliance of Automobile Manufacturers, a Washington advocacy group that represents Ford, GM, Toyota, Porsche and other auto makers. She says all the necessary tools and diagnostic data for any repair job are available online from individual auto makers, as well as from tool manufacturers like Snap-on Inc.

Mr. Lowe says mechanics aren't interested in auto makers' intellectual property.

"We don't want to know how to make their onboard computers. We want what's on those computers. That's what right-to-repair is all about," he says.

Beyond intellectual-property issues, Sandy Bass-Cors, executive director of the Coalition for Auto Repair Equality in Alexandria, Va., says mechanics are frustrated that the federal government spent billions of dollars bailing out GM and Chrysler during the recession, while boosting dealership sales with the Cash for Clunkers program.

"Yet they're keeping the same motoring taxpayers from having a choice in repairs," she says.

For now, Mr. Marconi says he's taking vehicles that need reprogramming to dealers himself, often at a loss, rather than send drivers away. "This is crazy," he says. "But in this economy the last thing you want to do is turn down a customer."