The noun (Substantiv/Nomen) Defekte is feminine in German. Therefore, the correct definite article in the nominative singular is die. So, you say: die Defekte.
(defects)
Mängel oder Fehler, die die Funktionstüchtigkeit beeinträchtigen.
Defects or flaws that impair functionality.
Das Auto hatte mehrere Defekte.
The car had several defects.