Vehicle almost failing to operate (3)
I believe the answer is:
bus
'vehicle' is the definition.
(bus is a kind of vehicle)
'almost failing to operate' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'failing to operate' becomes 'bust' (bust can mean broken or malfunctioning).
'bust' with its last letter taken off is 'BUS'.
(Other definitions for bus that I've seen before include "Coach" , "Something caught" , "Motor-coach" , "Charabanc" , "eg Double-decker" .)