Sham attempt back in vehicle (5)
I believe the answer is:
bogus
'sham' is the definition.
(thesaurus)
'attempt back in vehicle' is the wordplay.
'attempt' becomes 'go' (go is a kind of attempt).
'back' is a reversal indicator.
'in' is an insertion indicator.
'vehicle' becomes 'bus' (I've seen this before).
'go' reversed gives 'og'.
'og' put inside 'bus' is 'BOGUS'.
(Other definitions for bogus that I've seen before include "Pretended" , "Mock" , "Spurious" , "that's not real" , "Fake, phoney" .)