Sims 4 Mod Troubleshooting Guide

Everything you need to know about why Sims 4 mods break, how to find the problem, and how to fix it. Whether you have 50 mods or 15,000, this guide covers every common issue and solution.

Just had a patch break your game? Start with the latest Sims 4 patch page (which patch is out now, what changed, and a patch-day checklist), then come back here for the full method.

1. Why Mods Break After Updates

Sims 4 mods work by overriding or extending game files. Every mod is either a .package file (custom content, tuning overrides) or a .ts4script file (Python script mods). When EA releases a game patch, the internal files these mods depend on can change.

What changes in a patch

• Python modules — The game's core code lives in simulation.zip. When EA renames, removes, or restructures Python modules, any script mod that imports them will crash with an ImportError.
• Tuning resource IDs — Every game object, interaction, trait, and buff has a unique identifier. When these change, mods that override them either do nothing (pointing at a resource that no longer exists) or cause conflicts.
• XML structures — Tuning XML files define game behavior. When EA changes the expected fields or structure, mods with the old format can cause silent bugs or crashes.
• Game settings reset — Every patch automatically disables "Script Mods Allowed" in your game options. This is the #1 reason mods stop working after an update, and it's the easiest to fix.

Which mods are most at risk

• Script mods (.ts4script) — Highest risk. These run Python code that directly depends on the game's internal modules. Even small EA changes can break them.
• Tuning override mods (.package with XML) — Medium risk. These change game behavior by overriding tuning resources. Break when EA changes the underlying resource.
• Pure CC (.package, meshes and textures only) — Lowest risk. Custom hair, clothing, furniture, and objects rarely break because they add new content rather than overriding existing game files. Occasionally affected by catalog re-tags.

2. Types of Mod Problems

Broken script imports

A script mod tries to import a Python module that EA renamed or removed in a patch. The game crashes with Error 109 or a lastException traceback showing ImportError or ModuleNotFoundError.

Broken tuning overrides

A mod overrides a game tuning resource (interaction, buff, trait, etc.) that no longer exists in the current game version. This usually causes silent failures — things just stop working without an obvious error.

Mod conflicts

Two mods try to override the same game resource. Only one can win, and the other is silently ignored. This causes unpredictable behavior depending on which mod loads last.

Duplicate mods

Multiple copies of the same mod (different versions or exact copies in different subfolders) waste space and can cause version conflicts. Common if you've been downloading CC for years.

Corrupted files

Incomplete downloads, file transfer errors, or interrupted installations can leave you with corrupted .package or .ts4script files that the game can't read.

Cache staleness

The game caches compiled data from mods. After adding, removing, or updating mods, stale cache files can cause unexpected behavior. Clearing the cache forces the game to rebuild from fresh mod data.

3. First Steps When Your Game Won't Work

1. Re-enable mods. Go to Game Options → Other → check "Enable Custom Content and Mods" and "Script Mods Allowed." Every patch disables these automatically. Restart the game after enabling.
2. Clear your cache. Go to Documents/Electronic Arts/The Sims 4/ and delete localthumbcache.package and everything inside the cache/ folder. The game rebuilds these on next launch.
3. Test without mods. Temporarily move your entire Mods folder to your desktop. Launch the game. If it works, the problem is definitely a mod. If it still crashes, the problem is your game installation (try Repair Game in EA App/Origin).
4. Remove script mods first. Script mods cause the most crashes. Move all .ts4script files out of your Mods folder and test. If the game works, a script mod is the culprit.
5. Check for updates. Visit each mod creator's page (Patreon, ModTheSims, CurseForge, personal website) and check if they've released an update for the latest patch. Update timing varies by creator.

4. How to Read Crash Logs

When The Sims 4 crashes due to a mod, it usually writes a crash log to Documents/Electronic Arts/The Sims 4/. Here's how to find useful information in them.

lastException.txt / lastException.html

This file contains a Python traceback — a chain of function calls that shows what the game was doing when it crashed. What to look for:

• The last line of the traceback — this is the actual error. Common ones: ImportError, AttributeError, TypeError, KeyError.
• File paths containing mod names — look for paths that include words like .ts4script or mod names you recognize. That's your culprit.
• The "Traceback (most recent call last)" header — everything between this and the final error line is the call stack. Scan it for mod names.

Better Exceptions

Better Exceptions is a Sims 4 script mod. Better Exceptions can produce more readable reports and identify likely contributors. If you're doing any amount of mod troubleshooting, install it first.

Automatic crash log reading

Sims 4 Mod Fixer can read your crash logs, including the extra detail Better Exceptions adds to them and MC Command Center's exception log, and point to the mod each crash most likely came from. It saves you from reading tracebacks by hand, but treat the result as a strong lead rather than a verdict, and confirm it with a quick test.

5. The 50/50 Method

The 50/50 method is the traditional way to find a broken mod when you don't know which one is causing problems. It works, but it's slow.

How to do it manually

1. Create a temporary folder on your desktop called "Mods Backup"
2. Move half of your Mods folder contents into the backup folder
3. Launch the game and test if the problem is gone
4. If the problem is gone: the broken mod is in the half you removed. Move everything back, then move the other half out instead.
5. If the problem remains: the broken mod is still in your Mods folder. Move another half out.
6. Keep splitting in half until you find the specific mod
7. Repeat the entire process if you suspect multiple broken mods

How long it takes

Large Mods folders can require many testing rounds.

Tips for faster 50/50

• Start by removing all script mods first — they cause the most crashes and there are usually fewer of them
• Group mods by creator or source when splitting — if a creator's mods are outdated, multiple will be broken
• Keep recently downloaded mods as a separate group — newer downloads are more likely to be the issue if things were working before

6. Tools and Community Resources

Several tools and community sites exist to help with Sims 4 mod management. Here's what's available.

Troubleshooting Tools

Community Resources

7. Common Errors and Fixes

Error 109 / "Script call failed"

Cause: A script mod crashed. Error 109 can be caused by an outdated or incompatible script mod (.ts4script file).

Fix: Remove all script mods, re-enable script mods in settings, clear cache, add scripts back one at a time. Or use Sims 4 Mod Fixer to flag the likely broken script for you.

Infinite loading screen

Cause: Usually a corrupted save, broken mod, or stale cache. Can also be caused by a mod conflict on a lot you're loading.

Fix: Clear cache first. If that doesn't work, try loading a different household/lot. If it only happens on one lot, a mod is conflicting with something on that lot. Test without mods to confirm.

Game won't launch / black screen

Cause: Screen override mods, broken UI mods, or corrupted game files.

Fix: Remove all mods and test. If the game launches clean, add mods back in batches. Screen override mods (loading screen replacements, menu overhauls) are a common culprit after patches.

Missing CC in-game (red question marks)

Cause: The game can't find assets referenced by a mod. Usually means a .package file was removed or renamed but is still referenced by a save or tray file.

Fix: If you removed CC intentionally, the question marks will persist in lots/Sims that used it until you replace the items. Use Sims 4 Tray Importer to see which CC is used by which Sims/Lots.

"Mods and CC disabled" after every patch

Cause: EA automatically disables mod support after every game update as a safety measure.

Fix: Game Options → Other → check both "Enable Custom Content and Mods" and "Script Mods Allowed." Restart the game. This happens after every single patch — it's not a bug, it's by design.

Game is slow / lagging with mods

Cause: Too many tuning overrides, conflicting mods fighting each other, or heavy script mods running in the background.

Fix: Check for duplicates (having 3 copies of the same CC triples the loading work). Remove old mods you no longer use. Check if any script mods are known to be performance-heavy.

8. Preventing Future Problems

• Back up before every patch. Copy your entire Mods folder somewhere safe before updating the game. If mods break, you can restore and play on the old version while waiting for updates.
• Organize by type. Keep script mods in one subfolder and CC in another. When troubleshooting, you can quickly isolate script mods (which cause most crashes) from CC.
• Keep a mod list. Track where you downloaded each mod and what it does. When something breaks, you'll know where to check for updates.
• Update the big ones first. After a patch, check for updates to your most important script mods first: MC Command Center, Better Exceptions, UI Cheats Extension, Wicked Whims / Wonderful Whims.
• Update before you delete. A mod that breaks after a patch usually isn't dead — it's out of date. Check the creator's page first; if an update exists, that's almost always the fix. Only remove a mod outright if it's been abandoned (no updates in a year or more) or you've confirmed a newer alternative replaces it.
• Don't update the game on day one. If you have a lot of mods, consider waiting a little after a patch before updating so creators have time to respond. Update timing varies by creator. You can delay the update in EA App settings.
• Clear cache regularly. After adding, removing, or updating any mods, delete localthumbcache.package and the cache/ folder contents. Takes 10 seconds and prevents a lot of weird behavior.
• Run a health check after patches. Use Sims 4 Mod Fixer to check your mods against the new game version before you launch. Catching likely problems before they crash your game saves time. Keep an eye on the latest patch page for what each update changed.

Quick answers

Why do Sims 4 mods break after updates?

Sims 4 mods work by overriding or extending game files. When EA releases a patch, internal resource identifiers, Python modules, and tuning XML structures can change. Mods that reference the old versions of these resources will stop working or cause crashes. Script mods (.ts4script) are most vulnerable because they import specific Python modules from the game. Tuning mods (.package) break when the game resources they override are renamed, moved, or removed.

How do I do the 50/50 method for Sims 4?

The 50/50 method works by removing half your mods, testing the game, and repeating. Step 1: Move half your Mods folder contents to a temporary folder on your desktop. Step 2: Launch the game and test if the problem is gone. Step 3: If the problem is gone, the broken mod is in the half you removed. If the problem remains, it's in the half still in your Mods folder. Step 4: Take the half that contains the problem and split it in half again. Step 5: Repeat until you find the specific mod. Large Mods folders can require many testing rounds.

What does Error 109 mean in Sims 4?

Error 109 in The Sims 4 means the game crashed due to a script error. Error 109 can be caused by an outdated or incompatible script mod (.ts4script file). The most common fix is to remove all script mods, re-enable script mods in Game Options, clear your cache, and add script mods back one at a time. The lastException.txt file in your Sims 4 user data folder will contain details about which script caused the error.

How do I read Sims 4 crash logs?

Sims 4 crash logs are stored as lastException.txt or lastException.html files in Documents/Electronic Arts/The Sims 4/. Open the file and look for the 'Traceback' section — the last line before the traceback usually names the mod or script that caused the crash. If you use Better Exceptions, it generates more detailed crash reports that name the responsible mod directly. Sims 4 Mod Fixer can also read these crash logs automatically and point to the likely culprit mod.