A few brave movies did attempt to explain how and why a vehicle could turn evil. 1983's Christine centered around a 1958 Plymouth Fury that goes on a rampage because it has serious co-dependency issues with its owner, and the title vehicle of 1980's The Hearse went bad because it once transported the corpse of a Satanist.
Crown International Pictures
The final nail in the tire was Stephen King's directorial debut and farewell, 1986's Maximum Overdrive. In it, all of the world's vehicles and machines turn evil because of a passing comet, but also maybe aliens? Whatever, King was swimming in cocaine for most of that decade anyway.