Scrub clean, possibly, after starting the car (6)
I believe the answer is:
cancel
'scrub' is the definition.
(I know that scrub can be written as cancel)
'clean possibly after starting the car' is the wordplay.
'possibly' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'starting' says to take the initial letters.
The initial letter of 'car' is 'c'.
'clean' is an anagram of 'ancel'.
'ancel' put after 'c' is 'CANCEL'.
(Other definitions for cancel that I've seen before include "Delete" , "Officially prevent happening" , "Go for an annulment" , "Annul, revoke" , "Scrub" .)