diff --git a/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo1.java b/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo1.java
new file mode 100644
index 00000000..5b50fcfd
--- /dev/null
+++ b/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo1.java
@@ -0,0 +1,39 @@
+/* (c) https://github.com/MontiCore/monticore */
+package de.monticore.lang.sysmlv2.cocos;
+
+import de.monticore.lang.sysmlbasis._ast.ASTSpecialization;
+import de.monticore.lang.sysmlparts._ast.ASTPartUsage;
+import de.monticore.lang.sysmlparts._cocos.SysMLPartsASTPartUsageCoCo;
+import de.monticore.types.mcbasictypes._ast.ASTMCType;
+import de.se_rwth.commons.logging.Log;
+
+import java.util.stream.Collectors;
+
+/**
+ * CoCo1: Jeder in "part name:Typ" verwendete Typ muss eine existierende Part-Definition sein.
+ */
+public class MKPX_CoCo1 implements SysMLPartsASTPartUsageCoCo {
+
+  protected String printPartType(ASTMCType type) {
+    return type.printType();
+  }
+
+  @Override
+  public void check(ASTPartUsage node) {
+    var nonExistent = node.streamSpecializations()
+        .flatMap(ASTSpecialization::streamSuperTypes)
+        .filter(t ->
+            node.getEnclosingScope().resolvePartDef(printPartType(t)).isEmpty()
+        )
+        .collect(Collectors.toList());
+
+    for (var problem : nonExistent) {
+      Log.error(
+          "0xMKPX01 The type referenced in a PartUsage \"" + printPartType(problem)
+              + "\" does not exist as a part definition.",
+          node.get_SourcePositionStart(),
+          node.get_SourcePositionEnd()
+      );
+    }
+  }
+}
diff --git a/language/src/test/java/cocos/MKPXCoCo1Test.java b/language/src/test/java/cocos/MKPXCoCo1Test.java
new file mode 100644
index 00000000..9a1543fb
--- /dev/null
+++ b/language/src/test/java/cocos/MKPXCoCo1Test.java
@@ -0,0 +1,80 @@
+/* (c) https://github.com/MontiCore/monticore */
+package cocos;
+
+import de.monticore.lang.sysmlparts._cocos.SysMLPartsASTPartUsageCoCo;
+import de.monticore.lang.sysmlv2.SysMLv2Mill;
+import de.monticore.lang.sysmlv2._ast.ASTSysMLModel;
+import de.monticore.lang.sysmlv2._cocos.SysMLv2CoCoChecker;
+import de.monticore.lang.sysmlv2._parser.SysMLv2Parser;
+import de.monticore.lang.sysmlv2.cocos.MKPX_CoCo1;
+import de.se_rwth.commons.logging.Log;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class MKPXCoCo1Test {
+
+  private static final String MODEL_PATH = "src/test/resources/parser";
+
+  private SysMLv2Parser parser = SysMLv2Mill.parser();
+
+  @BeforeAll
+  public static void init() {
+    Log.init();
+    SysMLv2Mill.init();
+  }
+
+  @BeforeEach
+  public void reset() {
+    SysMLv2Mill.globalScope().clear();
+    Log.getFindings().clear();
+    Log.enableFailQuick(true);
+  }
+
+  @Nested
+  public class MKPXCoCo1Tests {
+    @Test
+    public void testValid() throws IOException {
+      String validModel =
+            "part def SubComponent1;"
+          + "part def SubComponent2;"
+          + "part def MainComponent{"
+          +   "part subcomp1: SubComponent1;"
+          +   "part subcomp2: SubComponent2;"
+          + "}";
+
+      ASTSysMLModel ast = SysMLv2Mill.parser().parse_String(validModel).get();
+      SysMLv2Mill.scopesGenitorDelegator().createFromAST(ast);
+      var checker = new SysMLv2CoCoChecker();
+      checker.addCoCo((SysMLPartsASTPartUsageCoCo) new MKPX_CoCo1());
+      checker.checkAll(ast);
+      assertTrue(Log.getFindings().isEmpty());
+    }
+
+    @Test
+    public void testInvalid() throws IOException {
+      String invalidModel =
+            "part def SubComponent1;"
+          + "part def MainComponent{"
+          +   "part subcomp1: SubComponent1;"
+          +   "part subcomp2: UndefinedComponent;"
+          + "}";
+
+      ASTSysMLModel ast = SysMLv2Mill.parser().parse_String(invalidModel).get();
+      SysMLv2Mill.scopesGenitorDelegator().createFromAST(ast);
+      var checker = new SysMLv2CoCoChecker();
+      checker.addCoCo((SysMLPartsASTPartUsageCoCo) new MKPX_CoCo1());
+      Log.enableFailQuick(false);
+      checker.checkAll(ast);
+      assertTrue(Log.getFindings().stream()
+          .anyMatch(f -> f.getMsg().contains("0xMKPX01")));
+    }
+  }
+
+}