The　key　objective　of　this　work　is　to　deal　with　the　fault　detection　issues　for　a　general　type　of　nonlinear　control　processes.　Firstly,　the　approximation　of　the　nonlinear　process　is　studied　based　on　a　set　of　Takagi-Sugeno　fuzzy　systems.　Then,　a　fuzzy　controller　based　on　an　observer　is　present　to　achieve　the　stability　of　the　nonlinear　process,　which　also　lays　the　basis　for　the　construction　of　the　image　representations　of　the　system　and　nominal　system.　With　the　image　representations,　the　input　and　output　signal　errors　are　obtained,　which　can　be　used　for　the　setting　of　the　evaluation　function.　By　handling　a　series　of　matrix　inequalities,　the　threshold　is　designed,　and　a　fault　detection　system　for　the　nonlinear　control　process　is　realized　with　the　decision　logic.　In　the　end,　an　illustration　example　is　given　to　validate　the　obtained　results.　©　2022　IEEE.