Dreadful to-do in vehicle, giving pet access (3,4)

'pet access' is the definition.
(door giving a cat access to a building)

'dreadful to-do in vehicle' is the wordplay.
'dreadful' is an anagram indicator.
'in' indicates putting letters inside.
'vehicle' becomes 'car' (car is a kind of vehicle).
'to'+'do'='todo'
'todo' with letters rearranged gives 'tdoo'.
'tdoo' going inside 'car' is 'CAT DOOR'.

'giving' acts as a link.