WASHINGTON/SAN FRANCISCO (Reuters) -U.S. safety regulators on Friday upgraded their probe into Tesla vehicles over power steering loss to the status of an engineering analysis - a required step before the agency could demand a recall. Tesla shares, which dropped more than 25% in January alone, fell more than 3% on Friday. The National Highway Traffic Safety Administration (NHTSA) said the investigation covered about 334,000 Model 3 and Model Y vehicles from the 2023 model year.