Protective coat is standard on car (5)
I believe the answer is:
parka
'protective coat' is the definition.
'parka' can be an answer for 'coat' (parka is a kind of coat). I am not sure about the 'protective' bit.
'standard on car' is the wordplay.
'standard' becomes 'par' (I've seen this before).
'on car' becomes 'ka' (I am not sure about this - if you are sure you should believe this answer much more).
'par'+'ka'='PARKA'
'is' is the link.
Can you help me to learn more?
(Other definitions for parka that I've seen before include "hoodie" , "Windproof jacket" , "Anorak" , "warm gear" , "Hooded weatherproof coat" .)