The One vehicle or the Buddha Vehicle is yi1 cheng4 fa3 in hanyu
pinyin
please edit after you post to avoid embarassment 
there's a few sutras that Buddha spoken without the disciples
asking, as they don't know to ask. when you read those sutras that
start with "fo suo...", they are all spoken without
asking.
Like the Lotus sutra, Brahma net sutra and Amitabha Sutra.
Amitabha's cultivations of pureland path is a Buddha-yana.
they are so profound that even Ven Shariputra (foremost in wisdom)
also not able to ask!
There are alot of sutra which start with Buddha said (fo
suo)
like Ullambana Sutta
actually a proper study of the teachings should be done before any
expert will point out mistake...
there are basically 12 categories of Buddha teaching method
one of them is indeed , "self-preach or zi suo " which ,because the
faculties of the ordinary ppl and arhat could not fathom the
inconceivable power of Buddha Amitabha ,so Buddha preach on
Amitabha Sutra
