The car fire was reported shortly around 5:45 a.m. on the northbound 5 Freeway near the Garfield Avenue exit.
The vehicle was on the shoulder fully engulfed, and flames were seen reaching nearby brush beside the freeway.
Firefighters quickly responded and appeared to extinguish the fire shortly after 6 a.m.
Two lanes were closed on the busy section of the freeway as crews worked to clean up the mess, which caused traffic to back up for miles all the way up to Buena Park. The freeway appeared to be back open shortly before 7 a.m.
The vehicle was not involved in a traffic collision, investigators said. It was not immediately known what caused the car to engulf in flames.
No injuries were reported in the incident.