After Leviathan!Sam and Leviathan!Dean go on a killing spree (while driving a 67 Impala) causing the real Sam and Dean to become America's 2nd most wanted criminals, Frank Devereaux advises the boys to lock up the Impala to avoid detection. At first they drive a Pontiac Acadian, then Dean steals a Dodge Challenger. After Bobby's death, Dean drives a Buick Special Deluxe and then, when he's in 1944, a Plymouth Roadking. After making it back to 2012, Sam and Dean drive a Buick Riviera, a Mercury Cougar, a Pontiac Firebird, and then a Dodge Charger.
The car is a 1970 Dodge Charger R/T 440. Meg refers to it as a junker, but it appears to be in good condition. Dean drives it from Indiana to Montana to Colorado and then back to Indiana when he's searching for a cure for Sam's sleepless condition. Emmanuel, aka amnesia! Castiel, and then later Meg are both his passengers on his last leg back to Indiana, where Castiel gets his memory back in time to save Sam. When Castiel first remembers who he is, he's distraught, but Dean reaches into the trunk of the Charger and pulls out his trench coat. It inspires Castiel to try to fix his past mistakes.