diff --git a/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo4.java b/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo4.java
new file mode 100644
index 00000000..ff9a357b
--- /dev/null
+++ b/language/src/main/java/de/monticore/lang/sysmlv2/cocos/MKPX_CoCo4.java
@@ -0,0 +1,96 @@
+/* (c) https://github.com/MontiCore/monticore */
+package de.monticore.lang.sysmlv2.cocos;
+
+import de.monticore.lang.sysmlbasis._ast.ASTEndpoint;
+import de.monticore.lang.sysmlparts._ast.ASTConnectionUsage;
+import de.monticore.lang.sysmlparts._cocos.SysMLPartsASTConnectionUsageCoCo;
+import de.monticore.lang.sysmlparts._symboltable.ISysMLPartsScope;
+import de.monticore.lang.sysmlparts._symboltable.PartDefSymbol;
+import de.monticore.lang.sysmlparts._symboltable.PartUsageSymbol;
+import de.monticore.symboltable.modifiers.AccessModifier;
+import de.se_rwth.commons.logging.Log;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * MKPX_CoCo4:
+ * In einer Verbindung "connect a.b to c.d" muss jeder verwendete (qualifizierte) Portname existieren.
+ */
+public class MKPX_CoCo4 implements SysMLPartsASTConnectionUsageCoCo {
+
+  @Override
+  public void check(ASTConnectionUsage node) {
+    if (!node.isPresentSrc() || !node.isPresentTgt()) {
+      return; // keine Verbindung
+    }
+
+    ISysMLPartsScope scope = node.getEnclosingScope();
+
+    checkEndpoint(scope, node.getSrc(), node);
+    checkEndpoint(scope, node.getTgt(), node);
+  }
+
+  protected void checkEndpoint(ISysMLPartsScope scope,
+                               ASTEndpoint endpoint,
+                               ASTConnectionUsage conn) {
+    String qname = endpointQName(endpoint);
+    if (qname.isEmpty()) {
+      return;
+    }
+
+    String[] parts = qname.split("\\.");
+
+    // Qualifizierter Name: a.b -> resolve a (PartUsage), dann b in PartDef
+    if (parts.length >= 2) {
+      String partName = parts[0];
+      String portName = parts[parts.length - 1];
+
+      Optional<PartUsageSymbol> partOpt = scope.resolvePartUsageLocally(partName);
+
+      if (partOpt.isEmpty()) {
+        // Existenz der Subkomponente wird bereits in MKPX_CoCo3 geprüft.
+        return;
+      }
+
+      var partDefOpt = partOpt.get().getPartDef();
+      if (partDefOpt.isEmpty()) {
+        // CoCo3
+        return;
+      }
+
+      PartDefSymbol partDef = partDefOpt.get();
+      boolean portExistsInDef = partDef.getSpannedScope()
+          .resolvePortUsageLocallyMany(false, portName, AccessModifier.ALL_INCLUSION, p -> true)
+          .size() == 1;
+
+      if (!portExistsInDef) {
+        Log.error(
+            "0xMKPX04 The port '" + portName + "' does not exist in the definition of subcomponent '"
+                + partName + "'.",
+            conn.get_SourcePositionStart(),
+            conn.get_SourcePositionEnd()
+        );
+      }
+    }
+    else {
+      // Unqualifiziert: Port der Oberkomponente muss lokal existieren
+      String portName = parts[0];
+      List<?> localPorts = scope.resolvePortUsageLocallyMany(
+          false, portName, AccessModifier.ALL_INCLUSION, p -> true);
+      if (localPorts.isEmpty()) {
+        Log.error(
+            "0xMKPX04 The port used in 'connect' '" + portName
+                + "' does not exist in the parent component.",
+            conn.get_SourcePositionStart(),
+            conn.get_SourcePositionEnd()
+        );
+      }
+    }
+  }
+
+  /** Liefert den qualifizierten Namen des Endpunkts als String. */
+  protected String endpointQName(ASTEndpoint ep) {
+    return ep.getMCQualifiedName() != null ? ep.getMCQualifiedName().toString() : "";
+  }
+}
diff --git a/language/src/test/java/cocos/MKPXCoCo4Test.java b/language/src/test/java/cocos/MKPXCoCo4Test.java
new file mode 100644
index 00000000..180aa5bd
--- /dev/null
+++ b/language/src/test/java/cocos/MKPXCoCo4Test.java
@@ -0,0 +1,84 @@
+/* (c) https://github.com/MontiCore/monticore */
+package cocos;
+
+import de.monticore.lang.sysmlparts._cocos.SysMLPartsASTConnectionUsageCoCo;
+import de.monticore.lang.sysmlparts._cocos.SysMLPartsASTPartDefCoCo;
+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_CoCo4;
+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 MKPXCoCo4Test {
+
+  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 MKPXCoCo4Tests {
+    @Test
+    public void testValid() throws IOException {
+      String validModel =
+          "part def A { port p: int; }"
+        + "part def B { port q: ~int; }"
+        + "part def System {"
+        +   "part a: A;"
+        +   "part b: B;"
+        +   "connect a.p to b.q;"
+        + "}";
+
+      ASTSysMLModel ast = SysMLv2Mill.parser().parse_String(validModel).get();
+      SysMLv2Mill.scopesGenitorDelegator().createFromAST(ast);
+      var checker = new SysMLv2CoCoChecker();
+      checker.addCoCo(new MKPX_CoCo4());
+      checker.checkAll(ast);
+      assertTrue(Log.getFindings().isEmpty());
+    }
+
+    @Test
+    public void testInvalid() throws IOException {
+      String invalidModel =
+          "part def A { port p: int; }"
+        + "part def B { port q: ~int; }"
+        + "part def System {"
+        +   "part a: A;"
+        +   "part b: B;"
+        +   "connect a.wrongName to b.q;"
+        + "}";
+
+      ASTSysMLModel ast = SysMLv2Mill.parser().parse_String(invalidModel).get();
+      SysMLv2Mill.scopesGenitorDelegator().createFromAST(ast);
+      var checker = new SysMLv2CoCoChecker();
+      checker.addCoCo(new MKPX_CoCo4());
+      Log.enableFailQuick(false);
+      checker.checkAll(ast);
+      assertTrue(Log.getFindings().stream()
+              .anyMatch(f -> f.getMsg().contains("0xMKPX04")));
+    }
+  }
+}