The Palo Alto, California, company said one of its cars had an abnormal amount of rust on a suspension part, a problem it hasn't seen in any other car.
On Thursday, the US National Highway Traffic Safety Administration said it asked for information from owners and Tesla about Model S suspension failures. The agency has not opened a formal investigation and said late Friday that the inquiry was a "routine data collection."
Tesla said the Model S with the rust had over 70,000 miles on it and was caked in dirt when picked up for service. The company said it has given the agency all relevant information.
NHTSA said Thursday that it was concerned that Tesla has asked owners to sign nondisclosure agreements about safety issues. The agency said it was concerned the agreements could prevent owners from reporting problems to the government. But it said Friday that Tesla has clarified the agreement language in a "satisfactory way" that resolves the issue.
Tesla said it has asked customers to sign a "Goodwill Agreement" when it agrees to fix a problem that wasn't the fault of the car. Those agreements make sure that repairing the car is not used against the company in court, Tesla said.
"This agreement never comes close to mentioning NHTSA or the government and has nothing to do with trying to stop someone from communicating with NHTSA," Tesla's statement said.
Shares of Tesla Motors Inc. closed Friday down $10.57, or 4.6 percent, to $218.79. They are down almost 13 percent over the past year.