The National Highway Traffic Safety Administration is looking into 2.56 million Tesla vehicles following a series of crashes involving the carmaker’s “Actual Smart Summon” feature.

Tesla introduced Actual Smart Summon, also known as ASS, last September with a software update. This feature allows Tesla owners to use their app to tell their vehicle to drive itself to them, using only the car’s cameras. The previous version, Smart Summon, also used ultrasonic sensors, which newer vehicles do not have.

The NHTSA’s Office of Defects Investigation (ODI) received a complaint about an ASS-related crash and has reviewed three media reports of similar incidents.

“All four incidents involve Tesla vehicles using [ASS] failing to detect obstacles and ending up in a crash,” the report states. The office also received 12 complaints related to Smart Summon, all describing crashes similar to those involving ASS and leaving drivers with little time to react.