Fan control doesn't work on Apple Silicon M3/M4+

[agoodkind]

Describe the bug

Manual fan control fails silently on Apple Silicon Macs with M3+. Setting a fan speed appears to succeed but the fan doesn't actually change. The system thermal daemon (thermalmonitord) immediately overrides the written value.

This happens because thermalmonitord enforces "protected mode" on fan control keys. Writes to F0Md (mode) and F0Tg (target) are blocked unless the Ftst (force/test) key is set to 1 first.

The current implementation writes directly to the fan mode and target keys without this coordination, so manual control never takes effect.

Screen.Recording.2026-01-23.at.13.33.26.mov

Technical context

• thermalmonitord holds fans in Mode 3 ("System Mode") by default, which blocks direct writes
• Writing Ftst=1 signals manual/test/force mode and causes thermalmonitord to yield control
• After unlock, mode writes must be retried until successful (typically 3-6 seconds)
• When returning all fans to automatic, Ftst=0 must be written to restore system control

See macos-smc-fan for detailed reverse engineering documentation.

Details:

• Device: All Apple Silicon Macs M3/M4+
• macOS: All versions on Apple Silicon
• Application version: All versions with fan control

[fernando-stahelin-civitas]

This is happening to me too

[Brtn11]

This does not happen to me on macOS sequoia 15.7.3 (24G419) with Apple M1 Pro.

[Ctepbluuka]

How can I fix it? On the first launch fans was started^ but on the second time it didn't. I use macOS 15.7.3 (24G419), Apple M1 Pro.

[Brtn11]

Hmm interesting. To be more specific, I also use macs fan control app and that also works. I installed a helper tool in both apps. Maybe deleting and reinstalling the helper app could help? You can find additional files from an app with app cleaner.

[Ctepbluuka]

Hmm interesting. To be more specific, I also use macs fan control app and that also works. I installed a helper tool in both apps. Maybe deleting and reinstalling the helper app could help? You can find additional files from an app with app cleaner.

Thanks! I use app cleaner and delete all files, reinstall and now it working

[agoodkind]

Updated issue to note that this issue has only been identified on M3+ Mac's but does not affect M1 and below. M2 untested.