From fault + -y.

• (British) IPA: /ˈfɒlti/, /ˈfɔːlti/
• (America) IPA: /ˈfɔlti/
  • (cot-caught) IPA: /ˈfɑlti/
• (Canada) IPA: [ˈfɒːlti]

faulty (comparative faultier, superlative faultiest)

1. Having or displaying faults; not perfect; not adequate or acceptable.

   They replaced the faulty wiring and it has worked fine ever since.

   I don't think you can infer that from the premise. It's a faulty argument.

   • 2017, David Walliams [pseudonym; David Edward Williams], Bad Dad, London: HarperCollins Children's Books, →ISBN:

     Sadly, the ever-eager Reverend Judith had not been able to conjure up many worshippers, even though it was Father’s Day. There was just one old dear sitting halfway back, her faulty hearing aid letting off a high-pitched whistle.

2. (obsolete) At fault, to blame; guilty.
   • 1590, Edmund Spenser, “Book II, Canto IV”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie, →OCLC ↗:

     Her faultie Handmayd, which that bale did breede, / Confest, how Philemon her wrought to chaunge her weede.

• faultless

• French: défectueux
• German: fehlerhaft, schadhaft
• Italian: difettoso, imperfetto, scorretto
• Russian: неиспра́вный
• Spanish: defectuoso, imperfecto