Vehicle part replaced (4)
I believe the answer is:
trap
'vehicle' is the definition.
(trap is a kind of vehicle)
'part replaced' is the wordplay.
'replaced' indicates anagramming the letters.
'part' is an anagram of 'TRAP'.
(Other definitions for trap that I've seen before include "fault" , "website?" , "that can let an actor down" , "Part (anag.)" , "Light carriage; ensnare" .)