It happened in Anaheim just after 8:30 a.m. Sunday in the 1500 block of W. Ball Road.
Anaheim police say a man exited the vehicle as responding officers approached it, and was taken into custody.
The body of a man was found inside the car suffering from what police are calling trauma, but further details of the victim's injuries and identity were not released.
The identity of the person detained has also not been made public, but the Anaheim Police Department says there is no search for additional suspects in this case, and there is no ongoing threat to the public.
Ball Road between Loara Street and Gilbuck Street in Anaheim was expected to be closed for the day due to the ongoing investigation.