How do I fix SimConnect errors in FSX?

Fix SimConnect errors in FSX or FSX: Steam Edition by reinstalling the specific side-by-side SimConnect runtime the add-on expects. Steam users should verify the game files and run the bundled RTM, SP1 and XPACK installers; boxed-FSX users should repair the simulator and its correct updates. Never download a loose SimConnect.dll.

Which SimConnect error are you seeing?

The wording of the error, and whether it affects one add-on or every client, usually identifies the right repair.

Why does FSX give me a side-by-side configuration error?

A side-by-side error means Windows could not load a versioned assembly required by FSX or the add-on; it does not automatically prove that SimConnect is missing.

Open Event Viewer, select Windows Logs > Application, and find the SideBySide event recorded at the failure time. If it names Microsoft.FlightSimulator.SimConnect, repair the corresponding SimConnect generation. If it names a Visual C++ CRT assembly, repair that exact x86 dependency instead of repeatedly reinstalling SimConnect.

Our procedure for identifying the missing FSX assembly with Event Viewer or sxstrace covers the detailed diagnosis.

Where can I download SimConnect for FSX?

For an FSX SimConnect download, use the installer already supplied with FSX, FSX: Steam Edition or the affected add-on; do not download a bare SimConnect.dll.

SimConnect is a versioned Windows runtime, not a standalone programme. Older add-ons may request the RTM, SP1 or Acceleration-era interface specifically, and those packages are designed to coexist. Installing XPACK does not make the lower-numbered clients obsolete.

• FSX: Steam Edition: use the legacy installers inside the FSX installation folder. Steam file verification restores them if they are missing.
• Boxed FSX: use the original simulator media and the update or Acceleration path belonging to that edition.
• Add-on-supplied prerequisite: use it only when it came with the add-on and its documentation calls for it.

A mistake we see constantly is copying a random DLL into the FSX root, System32 or SysWOW64. That bypasses the side-by-side registration SimConnect expects and can replace one visible error with crashes or another missing-assembly message. A DLL deliberately installed inside an add-on's own folder should be managed by that add-on's installer rather than deleted or replaced manually.

Do I need to install the FSX SDK?

No. The full FSX SDK is not required merely to run a normal SimConnect add-on or external utility. Developers and tools that explicitly require SDK components are the exception; the runtime installers can be used without setting up the complete SDK.

How do I repair SimConnect in FSX: Steam Edition?

Repair Steam Edition by verifying FSX and then running the legacy installer required by the add-on, or all three legacy installers if the required generation is unknown.

1. Close FSX and every connected programme. Exit weather engines, moving maps, hardware interfaces, flight recorders and any utility showing a connected or disconnected status.
2. Back up deliberately modified stock files. Steam verification may replace altered original files, although it does not normally remove separate add-on files.
3. Verify the FSX files in Steam. Open the game's properties and use the file-integrity verification option. This restores missing installer files but does not guarantee that every legacy runtime has been registered.
4. Browse to the real FSX installation folder. Do not assume it is on the Windows drive. Open SDK > Core Utilities Kit > SimConnect SDK > LegacyInterfaces.
5. Run the bundled installers. Open FSX-RTM, FSX-SP1 and FSX-XPACK, then run the SimConnect.msi in each required folder. If you do not know which one the add-on expects, install them in that order. Select Repair when Windows Installer offers it.
6. Test from a loaded flight. Start FSX, choose an aircraft, reach the cockpit and then launch the external client. This avoids confusing an early connection attempt with a damaged runtime.

The three legacy packages can remain installed together. Do not remove one merely because its version appears older, and never apply boxed-FSX service packs to Steam Edition. Our Steam Edition SimConnect installer locations and connection checks provide the edition-specific details.

How do I repair SimConnect in boxed FSX?

Boxed FSX must be repaired through its original simulator and update path because its SimConnect assemblies are installed by the base product, service packs and Acceleration.

1. Back up custom content and configuration files. Preserve aircraft, scenery, gauges and files you have edited before running a simulator-level repair.
2. Repair the base FSX installation. Use the original media's setup programme if it provides a repair option. A complete uninstall should be the last resort.
3. Restore the correct update level. A non-Acceleration installation normally follows the base FSX, SP1 and SP2 path. Acceleration or Gold Edition users should repair or reinstall Acceleration through its media rather than placing standalone SP2 over it.
4. Launch FSX once after the repair. Let the simulator finish creating or updating its configuration, close it, and then repair the affected add-on so its installer detects the restored FSX installation.

Windows may list several Microsoft Flight Simulator SimConnect Client entries after this process. That is normal: add-ons compiled for different FSX generations require those versions side by side. Removing every older entry can break an add-on that worked before the repair.

What if it gives me this error and the repair changes nothing?

A completed SimConnect repair that changes nothing usually means the wrong runtime was repaired or SimConnect was not the original fault.

Users sometimes describe this as “sigue igual” or “sí, pero no pasa nada”. Remember that SimConnect has no desktop shortcut, control panel or programme window. If SimConnect.msi completes and nothing opens afterwards, that is expected; the real test is whether the client connects to a loaded FSX flight.

Every local tool still says disconnected

If every same-PC client remains disconnected after the cockpit has loaded, test the default local connection before changing anything else.

1. Restart FSX without external utilities. Load a simple flight completely, then start one client manually.
2. Match Windows privilege levels. Run FSX and the client normally, or run both at the same elevated level. Running only one as administrator can interfere with some add-on launch and communication methods.
3. Set custom connection files aside. An ordinary same-PC connection does not normally need SimConnect.xml or SimConnect.cfg. Temporarily rename custom copies instead of deleting them. The active FSX configuration folder is commonly %APPDATA%\Microsoft\FSX; a side-by-side Steam installation may use %APPDATA%\Microsoft\FSX-SE.
4. Retest before restoring the files. If the client now connects, the runtime was working and the fault is in the custom protocol, address, port or XML syntax.

A client will also report Disconnected when FSX closes or crashes, so a simulator failure can be the cause rather than the result. For persistent cases, use our FSX event-log and SimConnect logging workflow to establish whether the server loaded and whether the client attempted a connection.

Only one add-on still fails

If another SimConnect client works, the shared runtime is functioning and the remaining fault belongs to the affected add-on or its launch configuration.

• Confirm that the add-on build supports FSX or FSX: Steam Edition, not a similarly named version intended only for another simulator.
• Repair the add-on with its original installer and verify that it detected the actual FSX folder.
• Start an external utility manually. If it connects manually but does not start with FSX, inspect exe.xml rather than repairing SimConnect again.
• For an in-process module that no longer loads, inspect dll.xml in the active FSX configuration folder. Back up and rename the file for testing; do not delete it.
• Check the add-on's own log for a missing dependency, licence failure or configuration error that merely appears alongside the SimConnect message.

Why does remote SimConnect remain disconnected?

A second-PC client remains disconnected when the FSX host and remote client disagree about the network protocol, host address or port, even if local SimConnect is working correctly.

The host's SimConnect.xml and the client's SimConnect.cfg must use matching settings. Allow FSX and the selected port through the private-network firewall, confirm that the client is using the host computer's address rather than its own, and check whether the host's local IP address changed after a router restart.

Our second-PC configuration guide for FSX tools explains the matching XML, client configuration, port and firewall checks.