Men supporting annual check for car (5)
I believe the answer is:
motor
'for car' is the definition.
(motor can informally mean a car)
'men supporting annual check' is the wordplay.
'men' becomes 'OR' (military abbreviation for Other Ranks).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'annual check' becomes 'mot' (MOT test for a vehicle).
'or' put after 'mot' is 'MOTOR'.
(Other definitions for motor that I've seen before include "Make good progress" , "Car; travel quickly" , "Travel by car, engine" , "Car (informal)" , "go quickly" .)