Tesla’s Full Self-Driving system is facing an expanded investigation by the National Highway Traffic Safety Administration over its safety during poor road visibility conditions, as previously reported by Reuters. Tesla vehicles with Full Self-Driving (FSD) have a “degradation detection” system that’s supposed to alert drivers to take over when the vehicle’s cameras can’t see the road clearly enough to safely use FSD, like during poor weather.

NHTSA’s Office of Defects Investigation (ODI) is now conducting an engineering analysis, which is the second and final phase of an investigation before a possible recall, to investigate whether the degradation detection system performs as advertised following numerous safety incidents.

According to a March 18th NHTSA filing, the degradation detection system “fails to detect and/or warn the driver appropriately under degraded visibility conditions such as glare and airborne obscurants. In the crashes that ODI has reviewed, the system did not detect common roadway conditions that impaired camera visibility and/or provide alerts when camera performance had deteriorated until immediately before the crash occurred.”

Tesla began developing an update for the degradation detection system in 2024 after a fatal 2023 incident, but Wednesday’s NHTSA filing states that the ODI doesn’t know which vehicles have received the update. However, the update may have been able to prevent some of the safety incidents the ODI is investigating.