Relinquish control of car, following shock (4,1,4,4)
I believe the answer is:
take a back seat
'relinquish control' is the definition.
(to take a back seat is to give up control)
'car following shock' is the wordplay.
I cannot quite understand how this works, but
'car' could be 'seat' (type) and 'seat' is located in the answer.
'shock' could be 'takeaback' (taken aback means shocked) and 'takeaback' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
(Other definitions for take a back seat that I've seen before include "from behind sofa?" , "let others do the work" , "Play second fiddle" , "Let others lead" , "Some drivers do" .)