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1.
A person willing to learn and perform scheduled maintenance or simple repairs on their own vehicle rather than being completely reliant on technicians who may be dishonest, careless, or ignorant.

Many automakers have realized that dealer service is profitable and have designed vehicles to be irreparable by independent or shade tree mechanics.
by Aguirrez May 19, 2008
 
2.
Anyone, while trying to fix an automobile, actually does more damage instead of fixing the problem
Doug is a Shade Tree Mechanic because he done broke his car again
by Brian O'Connor July 24, 2006