too vs to a fault

too and to a fault both are adverbs.

Word	Noun	Adjective	Verb	Adverb
too	No	No	No	Yes
to a fault	No	No	No	Yes

As adverbs, too and to a fault are synonyms defined as:

Other synonyms of too include excessively, overly.

too (adverb)	to a fault (adverb)
to a degree exceeding normal or proper limits	to a degree exceeding normal or proper limits
in addition