from my experiences Toyota plastics are usually sold without primer on it. also their plastics are usually the cars you see on the road with the paint falling off it.

i also forgot to add.
if there isn't primer on it. DON'T aggressively sand it.
if you sand with a red scotch brite and spray with adhesion promoter will swell up the scratches and create a BIG mess.
use the least aggressive scotch brite you can find.
i use the PPG 3 step one choice plastic prep system. this is the best plastic prep system on the market today. the su4901 plastic cleaner has a green scotch brite bonded to a sponge. the su4902 adhesion wipe and the su4903 adhesion promotor spray. i haven't ever seen or heard of a adhesion problem when using it in 15 years. the su4903 has been replaced with a newer product. i don't have the # for it.


i would add CLEANLENESS of PP based plastic is extremely important when prepping to paint.
before the SU system was developed i used to use clean with a gray scotch brite and white wall cleaner. i would rinse down with water, spray with WW cleaner, LIGHTLY scrub with a gray scotch brite and rinse. blow dry and apply adhesion promoter ASAP, best results if applied within 15 min after washing it down. PP plastic has wax as part of it's chemistry. the wax floats to the top when it contacts to the air. this is the biggest reason why the paint falls off this plastic. the WW cleaner removes this wax on the surface and lets the AP bite into the plastic.