WASHINGTON (Reuters) -U.S. safety regulators have upgraded their probe into Tesla vehicles over power steering loss to an engineering analysis - a required step before the agency could demand a potential recall. Tesla did not immediately respond to a request for comment. NHTSA, which had opened a preliminary evaluation in July into loss of steering control in 280,000 Tesla Model 3 and Y vehicles, said it had identified 2,388 total complaints, with some reporting an inability to turn the steering wheel, while others reported an increase in required effort to turn the steering wheel.