A fan of Tesla might think that the automaker just can’t catch a break when it comes to its autonomous driving tech. It’s already subject to several federal investigations over its marketing and deployment of technologies like Autopilot and Full Self-Driving (FSD), and as of last week, we can add another to the list involving around 2.4 million Tesla vehicles. This time, regulators are assessing the cars’ performance in low-visibility conditions after four documented accidents, one of which resulted in a fatality.

The National Highway Traffic Safety Administration (NHTSA) says this new probe is looking at instances when FSD was engaged when it was foggy or a lot of dust was in the air, or even when glare from the sun blinded the car’s cameras and this caused a problem.

What the car can “see” is the big issue here. It’s also what Tesla bet its future on.