Vehicle returned before end of warranty for service (4)
I believe the answer is:
navy
'service' is the definition.
(navy is a kind of service)
'vehicle returned before end of warranty' is the wordplay.
'vehicle' becomes 'van' (van is a kind of vehicle**).
'returned' says the letters should be written backwards.
'before' is a charade indicator (letters next to each other).
'end of' suggests the final letters.
The final letter of 'warranty' is 'y'.
'van' in reverse letter order is 'nav'.
'nav'+'y'='NAVY'
'for' is the link.
(Other definitions for navy that I've seen before include "military arm" , "Armed force" , "Ships-of-war" , "A dark blue; service" , "Fleet of ships" .)