Car performed function it had learnt by itself (10)
I believe the answer is:
autodidact
'it had learnt by itself' is the definition.
The definition suggests a singular noun which matches the answer.
'car performed function' is the wordplay.
'car' becomes 'auto' (automobile).
'performed' becomes 'did' ('do' can be a synonym of 'perform').
'function' becomes 'act' (I've seen this in another clue).
'auto'+'did'+'act'='AUTODIDACT'
Can you help me to learn more?
(Other definitions for autodidact that I've seen before include "learner without instructor" , "Self-taught person" , "person who taught himself" , "Self-educator" , "For one not needing instructor" .)