Check-up of a vehicle or a machine (5)
I believe the answer is:
motor
'a machine' is the definition.
(I know that motor is a type of machine)
'check-up of a vehicle' is the wordplay.
'check' becomes 'MOT' (MOT check for a vehicle).
'up of' says the letters should be written backwards (I've seen 'upped' mean this (in down clue, made to go up)).
'a vehicle' becomes 'ro' (I am not sure about this - if you are sure you should believe this answer much more).
'ro' written backwards gives 'or'.
'mot'+'or'='MOTOR'
'or' is the link.
Can you help me to learn more?
(Other definitions for motor that I've seen before include "(Transport using) engine" , "Car (colloq,)" , "Driver" , "Internal combustion engine" , "Car; powered machine" .)