A federal agency's investigation of problems with Tesla's Full Self-Driving just took a significant step forward. It could become a big problem for the stock.

The NHTSA is expanding its investigation into how safe Full Self-Driving is under less-than-ideal road conditions.

National Highway Traffic Safety Administration officials deepened their probe of Tesla’s driver-assistance system after the federal agency received reports of multiple crashes.

Investigation now covers 3.2 million vehicles as regulators examine crashes tied to reduced camera performance.

Technology Technology   The Big Story Tesla’s self-driving software under scrutiny The National Highway Traffic Safety Administration (NHTSA) intensified its investigation

Federal safety regulators escalate the investigation of Tesla's self-driving assistance technology after crashes and visibility issues.