Tesla (TSLA) is facing another setback with its Autopilot software, a system that CEO Elon Musk is betting on to power his robotaxi future.

The National Highway Traffic Safety Administration (NHTSA) said on Friday it was opening an investigation following Tesla’s recall of virtually every vehicle equipped with the automaker’s Autopilot advanced driver assistance systems. The original recall, a software update issued back in December, covered over 2 million Tesla vehicles and was meant to address “driver misuse” of the system, meaning Tesla had to add features that would make sure drivers were paying attention while operating Autopilot.