From fault + -ful.

faultful

1. With faults or sins; not perfect; flawed.

   Synonyms: fallible, imperfect

   Antonyms: faultless, infallible, perfect

   • 1594, William Shakespeare, Lucrece (First Quarto), London: […] Richard Field, for Iohn Harrison, […], →OCLC ↗:

     So fares it with this faultful lord of Rome,
     Who this accomplishment so hotly chas'd;
     For now against himself he sounds this doom,
     That through the length of times he stands difgrac'd

• German: fehlerhaft