"The front of the car just dropped," he said. "The left front wheel just detached from the car."

When Tesla picked up his car, Cordaro was at first told he would have to pay for the repairs because they were from normal wear. After pressing his case with a Tesla manager, he was told the company would pay part of the cost - as long as he signed a nondisclosure agreement.

Neither the equipment breakdown nor the confidentiality demand turned out to be an isolated case. And now they have Tesla Motors on the defensive.

After the nation's top auto safety regulator raised questions about reports of suspension problems with the Model S, Tesla declared in a blog post Friday that the suspension system had no safety defects. But what set the case apart from other auto safety episodes was the introduction of a nondisclosure agreement into the relationship between car owner and automaker - an unusual practice by an unconventional company whose founder, Elon Musk, has roots in Silicon Valley, not Detroit.

The company acknowledged having had car owners sign such agreements and said it did so to protect itself from potential lawsuits after performing a repair at a discount or at no charge.

'Troublesome' agreements

But the practice has raised concerns that it could prevent owners from reporting safety problems to the National Highway Traffic Safety Administration, which called Tesla's use of such agreements "troublesome" and told the company not to use terms that dissuade people from reporting safety concerns to the agency.

On Friday, a Tesla spokeswoman said in an email that "to remove any doubt," the automaker would modify the language of the documents to make clear that the goal "is to benefit customers, while not harming us for doing a good deed." She did not elaborate on how it would be changed.

The safety agency said in a statement that the changes were satisfactory, without elaborating. It described its review of the Model S suspension as "a routine data collection," adding that it had not found any safety issues so far and that Tesla was cooperating.

In agreements like the one Cordaro signed, Tesla refers to the repairs as a "gesture of goodwill," made without "any admission of liability or wrongdoing or acceptance of any facts."

That statement alone is uncontroversial. It is standard legalese protecting Tesla from admitting any wrongdoing by way of making a repair, said David Vladeck, a law professor at Georgetown University and a former director of the Federal Trade Commission's Bureau of Consumer Protection.

Muzzling consumers

But he said two other provisions in the contract were problematic in that they seemed to muzzle consumers: asking car owners to waive the right to future legal action and to keep the entire incident confidential.

"You agree to keep confidential our provision of the good will, the terms of this agreement and the incidents or claims leading or related to our provision of the good will," the Tesla document said.

Tesla said it was "preposterous" to suggest that it was trying to prevent owners from reporting safety problems to the NHTSA or any other government agency. But Vladeck said that distinction was unimportant. "Most reasonable consumers would interpret this as a provision prohibiting them from talking to anyone, including government or lawyers or anybody else," he said.

Tesla was founded in 2003 with the idea of establishing battery-powered cars as a viable emissions-free replacement for the internal combustion engine and challenging many auto industry conventions. It sells cars directly to customers without franchised dealers, a practice that has led to legal battles in several states.

The company is also building a gigantic battery factory in Nevada and often announces news in Twitter posts by Musk.

The use of nondisclosure agreements with customers appears to be highly unusual in the auto industry. Ford, General Motors and Toyota all said they did not have customers sign confidentiality agreements in exchange for fixing cars that have broken down.

Joan Claybrook, a former head of the NHTSA, said requiring customers to keep quiet about repairs aroused suspicion. "I don't know why they'd do that," she said. "It makes it seem like they want to cover something up."

'Toothless'

Leonard Lance, a Republican representative from New Jersey, introduced legislation in US Congress in April that would prevent companies from including nondisclosure clauses in consumer contracts. California, where Tesla is based, enacted a similar law in 2014.

News of Cordaro's breakdown and the nondisclosure agreement he signed was trumpeted by auto bloggers tracking suspension problems in the Model S, a luxury sedan whose pricing starts at about $US70,000.

The NHTSA website lists 33 complaints received since October about suspension failures in the car, Tesla's top-selling model.

Cordaro, an auto enthusiast who used to make hot rod cars, said Friday that he did not think the agreement barred him from talking to the safety agency or anyone else about the breakdown his car suffered in late April. When he reviewed it, Cordaro concluded that "it was basically toothless," he said. "It only keeps me from talking about the costs and filing a lawsuit."

Once his car was repaired and returned, he filed details of his suspension issue with the safety agency and a few weeks later got the broken ball joint from Tesla and sent it on to the NHTSA.

But he was nevertheless upset with how Tesla has dealt with what he thinks could pose a serious safety concern. "If it had happened on the highway, it could have been catastrophic," Cordaro, 61, said by phone while driving his Model S.

Cordaro said he was further annoyed because Tesla, in its blog post about the Model S suspension and confidentiality agreements, suggested his breakdown had resulted from hard driving.

The company said he lived on a long dirt road and noted that his car was "caked with mud" when it was picked up - information that Cordaro called "a fabrication."

"I wasn't out four-wheeling in the car," he said. "I live on an asphalt road and have maybe driven on dirt roads 10 times."

A Tesla spokeswoman said the company was looking into the matter.

The New York Times