Check car will be on time (5)
I believe the answer is:
'check' is the definition.
(an audit is an examination or check)
'car will be on time' is the wordplay.
'car' becomes 'audi' (Audi is a German car brand).
'will be on' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'time' becomes 't' (abbreviation).
(Other definitions for audit that I've seen before include "vetting of books" , "Official inspection of company accounts" , "Financial inspection" , "Formally examine" , "Stocktake" .)