As of October 23, 2026, in Assetto Corsa (1.16.x with Content Manager and Custom Shaders Patch), mods that don’t work almost always come down to one of these causes: the folder is in the wrong place, the mod needs a newer (or older) version of CSP, content it depends on is missing, or one of the mod’s files is corrupted. The first thing to do is check the logs in Documents\Assetto Corsa\logs (log.txt, errors.txt and custom_shaders_patch.log) and test with an official KUNOS car and track: if that loads, the problem is a specific mod.
Symptom, cause and fix
| What happens | Likely cause | What to do |
|---|---|---|
| The car or track doesn’t show up | An extra folder (content\cars\mod\car) | Put data.acd or data and the .kn5 files directly in its folder |
| Content Manager shows «Race cancelled» when you click Drive | The game crashed while loading; generic message | Read log.txt and errors.txt |
| Track with weird textures or strange lighting | It requires a newer version of CSP | Update CSP |
| Crashes on load since a CSP update | Incompatibility with the new version | Roll back one or two versions |
| You can’t join a server | Your content doesn’t match the server’s (checksum) | Install the same version of the car and track |
| The game crashes mid-race with an app active | Incompatible Python app or plugin | Disable apps and plugins, then re-enable them one by one |
Step 1: read the logs
Assetto Corsa stores its logs in Documents\Assetto Corsa\logs. The three that matter:
- log.txt: the full session log. Look at the last lines before the crash.
- errors.txt: the errors the game has detected.
- custom_shaders_patch.log: only if you use CSP; it records CSP’s errors.
They’re overwritten every time you start a session, so open them right after the failure. Look for the name of a car, a track or a .kn5 file: if it shows up near the error, reinstall that mod. A crash usually leaves a trace in log.txt starting with «CRASH in:». If you see «INVALID STATE RESET» repeated before it, there’s a case documented by server admins that’s fixed in Content Manager by setting «Game starter» to «Official».
Step 2: test with official content
Pick a KUNOS car and track, in practice mode with no AI opponents. If it loads, the game and CSP are fine and the problem is the modded car or track you were using: test each one separately with official content to find out which of the two it is. If even that won’t load, the problem runs deeper: CSP, an app or the game files.
Step 3: CSP, Sol and Pure
Many modern cars and tracks need Custom Shaders Patch: without it they look wrong or don’t load. But every CSP version changes things, and that’s where a good share of crashes come from:
- If a track requires a minimum CSP version (its author will say so), install that one or a later one from the CSP settings in Content Manager.
- If the game started crashing right after you updated CSP, roll back one or two versions.
- To rule it out completely, disable CSP and test with official content.
- Weather and graphics mods depend on specific versions: Sol only works with older CSP versions, and Pure requires a recent one. Use one or the other, not both.
Step 4: isolate the broken mod
In Assetto Corsa you don’t load every mod at once: only the ones you pick for the session, plus whatever apps and filters you have active. That’s why the half-and-half method mostly applies to apps and extras:
- Back up the folders you’re going to touch.
- Disable half of the Python apps and plugins in Content Manager and test.
- If the problem persists, the culprit is in the active half; if it goes away, it’s in the other half. Split again.
- Repeat until you find the app or plugin causing the crash.
With cars and tracks, change only one thing at a time (a different car on the same track, and vice versa). The order server admins suggest, from least to most drastic, is: reinstall the modded content you’re using (apps included), update CSP or roll it back one or two versions, disable CSP, disable plugins and apps, and restart your PC. If nothing works, a clean reinstall is usually faster.
Online errors: checksum
To join a server you need the same content it has: if your version of the car or track is different, the server rejects you on checksum, and sometimes it looks like a crash. Content Manager shows you what you’re missing and sometimes downloads it. Download the exact version the server or its community specifies.
Prevention
- Install with Content Manager by dragging the file onto its window, and check what it detects before clicking Install.
- Always download from the author’s page: «free paid» cars from reupload sites often come broken or modified.
- Before updating CSP, note down which version you had in case you need to go back.
More Assetto Corsa guides: how to install mods, servers, the best mods and PC requirements.
Frequently asked questions
What does «Race cancelled» mean in Content Manager?
It means the game closed before it finished loading or shortly after starting. It’s a generic warning: the real cause is in log.txt and errors.txt, in Documents\Assetto Corsa\logs.
Why doesn’t a modded car show up?
Almost always because of an extra folder. Inside content\cars\car_name you need the data.acd (or the data folder) and the .kn5 files directly.
Do I need CSP for every mod?
Not for all of them, but you do for many modern cars and tracks and for mods like Sol or Pure. If a track looks wrong, CSP is usually missing or out of date.
What do I do if the game crashes after updating CSP?
Go back to the previous version from Content Manager. If the problem goes away, wait for the mod author or the CSP author to fix it.
Where is the Assetto Corsa log?
In Documents\Assetto Corsa\logs: log.txt, errors.txt and, if you use CSP, custom_shaders_patch.log.