India, April 27 -- The US's top auto-safety regulator extended its years-long investigation of Tesla Inc.'s Autopilot to determine whether a fix the carmaker made months ago does enough to keep people from misusing the system. The National Highway Traffic Safety Administration disclosed Friday that it's opened a query into the Autopilot recall Tesla conducted in December.

The agency is concerned as to whether the company's remedy was sufficient, in part due to 20 crashes that have occurred involving vehicles that received Tesla's over-the-air software update.

More than 2 million Tesla vehicles are subject to the probe, according to NHTSA. The carmaker's shares fell as much as 2.2 per cent as of 3:30 p.m. New York time and are down more ...