How to Fix Assetto Corsa Error x4fab 21002 – Online Connection Issue Guide

Assetto Corsa error x4fab: 21002 appears when the game fails to complete an online connection handshake. The issue usually comes from a Custom Shaders Patch mismatch, Content Manager cache problems, blocked network traffic, or a broken multiplayer server session.

This guide shows the fastest working fixes in the correct order. Follow each step and test the game before moving to the next fix.

Step 1 — Restart Steam and Content Manager

Temporary network sessions sometimes lock up after sleep mode, updates, or crashes.

1. Close Content Manager completely.
2. Exit Steam from the system tray.
3. Reopen Steam.
4. Launch Content Manager.
5. Try joining the server again.

If the error continues, move to the next step.

Step 2 — Update or Roll Back Custom Shaders Patch

Most multiplayer connection errors come from CSP version conflicts.

Update CSP

1. Open Content Manager.
2. Go to Settings → Custom Shaders Patch → About & Updates.
3. Click Check for updates.
4. Install the latest stable version.
5. Restart Content Manager.

Roll Back CSP (If the error started after a recent update)

1. Open the CSP version selector.
2. Select a previous stable build.
3. Click Install.
4. Restart Content Manager.
5. Try connecting again.

Step 3 — Verify Assetto Corsa Game Files

Corrupted or missing game files can break multiplayer initialization.

1. Open Steam Library.
2. Right-click Assetto Corsa → Properties.
3. Open Installed Files.
4. Click Verify integrity of game files.
5. Wait for verification to finish.
6. Launch the game and test multiplayer.

Step 4 — Disable VPN and Firewall Filtering

VPNs and aggressive firewalls often block multiplayer handshake traffic.

1. Turn off any active VPN or proxy software.
2. Temporarily disable third-party firewalls or network filters.
3. Launch Assetto Corsa and retry the connection.

If the connection works, add Assetto Corsa and Content Manager to your firewall allow list.

Step 5 — Reset Content Manager Network Cache

Corrupted cached network files can prevent successful server connections.

1. Close Content Manager.
2. Open this folder:

Documents\Assetto Corsa\Config

3. Delete the file:

server_cfg.ini

(if it exists)

4. Restart Content Manager.
5. Try connecting again.

Step 6 — Test Another Multiplayer Server

Some servers run incompatible CSP versions or broken configurations.

1. Join a different public server.
2. Check whether the error appears on all servers or only one.

If the error happens only on one server, the issue sits on the server side.

Why Error x4fab: 21002 Happens

This error usually occurs when:

• The installed CSP version does not match server requirements.
• Content Manager network cache becomes corrupted.
• VPN or firewall blocks multiplayer traffic.
• Steam networking fails to refresh properly.
• The multiplayer server runs unstable or outdated configuration.

Fixing the connection layer resolves the problem in most cases.

What to Do If the Error Still Appears

If none of the steps solve the issue:

• Reinstall Custom Shaders Patch.
• Reinstall Content Manager only (keep your mods and tracks).
• Restart your PC and router.

These steps reset corrupted configuration layers without affecting your game library.

FAQs

What is Assetto Corsa error x4fab 21002?

Assetto Corsa error x4fab 21002 means the game failed to complete an online server connection handshake.

What causes error x4fab 21002 in Assetto Corsa?

A CSP version mismatch, blocked network traffic, corrupted Content Manager cache, or server-side issues usually trigger this error.

Does updating Custom Shaders Patch fix error x4fab 21002?

Yes, installing a compatible stable CSP version often resolves the connection failure immediately.

Can a VPN cause Assetto Corsa error x4fab 21002?

Yes, VPNs and network filters can block multiplayer handshake traffic and trigger this error.

Does verifying game files help fix error x4fab 21002?

Yes, Steam file verification repairs corrupted files that may block multiplayer initialization.

Is error x4fab 21002 a server problem or PC problem?

If the error appears on only one server, the issue is server-side; if it happens everywhere, it is local.

Do I need to reinstall Assetto Corsa to fix error x4fab 21002?

No, updating CSP and resetting Content Manager usually fix the issue without reinstalling the game.

Can outdated Content Manager cause error x4fab 21002?

Yes, outdated or corrupted Content Manager files can disrupt online connectivity.