The National Highway Traffic Safety Administration (NHTSA) closed an investigation into Fiat Chrysler on Jan. 5, 2016, after determining that non-Fiat Chrysler entertainment units weren't vulnerable to hacking, according to documents posted to

The department launched the investigation last July 24 after a pair of security researchers remotely controlled a Jeep once they accessed the engine, transmission, wheels and brakes among other systems all through the vehicle's UConnect “infotainment unit.” 

The NHTSA found that infotainment units sold to other companies by Harman International, the manufacturer of UConnect, weren't vulnerable to attack. The agency also worked with Sprint, Fiat Chrysler's wireless provider, to block access to a radio communications port unintentionally left open, the documents said. 

The agency also looked into 30 consumer complaints alleging the vulnerability had been exploited in other vehicles but was unable to confirm any of them.