A sign inside the Humming Motors auto repair shop says, "We do the worrying so you don't have to."

These days, owner David Baur spends a lot of time worrying in his full-service garage near downtown Los Angeles.

As cars become vastly more complicated than models made just a few years ago, Baur is often turning down jobs and referring customers to auto dealer shops. Like many other independent mechanics, he does not have the thousands of dollars to purchase the online manuals and specialized tools needed to fix the computer-controlled machines.

Baur says the dilemma has left customers with fewer options for repair work and given automakers an unfair advantage.

"When I was younger, I kept going until I solved the problem," the weary mechanic said as he wiped grease from his hands while taking a break. "Lately I find myself backing out. I'm more reluctant to take complex jobs on."

Access to repair information is at the heart of a debate over a congressional bill called the Right to Repair Act. Supporters of the proposal say automakers are trying to monopolize the parts and repair industry by only sharing crucial tools and data with their dealership shops. The bill, which has been sent to the House Committee on Energy and Commerce, would require automakers to provide all information to diagnose and service vehicles.

Automakers say they spend millions in research and development and aren't willing to give away their intellectual property. They say the auto parts and repair industry wants the bill passed so it can get patented information to make its own parts and sell them for less.

"Coke doesn't give away the recipe for Coke," said Charlie Territo, a spokesman for the Alliance of Automobile Manufacturers. "What this bill seeks to get is the recipe for Coke."

Many new vehicles come equipped with multiple computers controlling everything from the brakes to steering wheel, and automakers hold the key to diagnosing a vehicle's problem. In many instances, replacing a part requires reprogramming the computers _ a difficult task without the software codes or diagrams of the vehicle's electrical wires.

Mechanics say repair information gets constantly updated so they must know how to find answers amid the sometimes overwhelming amount of data. Keeping up with technology has become almost a part-time job and requires thousands of dollars to get the right tools and online manuals for each model.

"Doctors have it easy because the human body doesn't change model every year," said Paul Brow, owner of All-Car Specialists, a 30-year-old shop in suburban San Gabriel.