MacBook Pro fan always on — diagnose it

Your MacBook Pro fan never stops spinning. It’s not loud exactly — just always audible, with the occasional ramp-up. There’s almost certainly a process keeping the chip warmer than it needs to be. The fan isn’t the problem; whatever’s making the heat is.

Two patterns

The fan-always-on case usually breaks into two patterns:

• Low constant fan — fans running at 2500-3500 RPM all the time. Usually means a process at 20-40% CPU sustained, or a hot environment.
• Cycling fan — ramps up to high RPM, drops, ramps again every 1-3 minutes. Usually means a process spiking on a schedule (sync, indexer, cron job).

Identifying which pattern you have narrows the diagnosis.

Find the heat source

1. Open Activity Monitor, CPU tab. Sort by %CPU. Watch for two minutes. Note anything sustained over 10% CPU.
2. Check the Energy tab. Sort by "Energy Impact (12 hours)." The top entries are what's been keeping the chip awake.
3. Get a temperature reading: sudo powermetrics --samplers smc -i 1000 -n 5. Anything sustained over 65C will keep fans elevated.
4. Check fan RPM and temp together. The powermetrics output shows fan speed alongside die temp.
5. Run pmset -g assertions to see what's preventing the system from sleeping or going to low-power states.

Common culprits on MacBook Pro

• An external display, especially over USB-C, can keep the GPU active and warm
• Docker Desktop, even idle, holds processes that warm the SoC
• Antivirus or endpoint-management software scanning continuously
• A browser tab with autoplay video or background mining
• Bluetooth audio keeping the radio busy
• A failing fan sensor (rare; the system overcompensates by running fans high)

Fix it

Once you know the source:

• Quit and relaunch user apps that are misbehaving
• For sync agents, pause them temporarily to confirm they’re the cause
• For external displays, disconnect briefly and watch the fan
• For Docker, fully quit it (not just close the window) and confirm
• For sustained system daemons doing legitimate work, let them finish

When it really is the fan

If everything shows light load, the chip is cool (under 50C), and the fans are still high — the fan controller or a temperature sensor may be faulty. Apple Diagnostics (hold D at boot on Intel; specific keys on Apple Silicon) can flag thermal sensor issues. Service is the answer at that point.

Watching it live

The fan-vs-temperature correlation is easier to see continuously than in spot checks. Beacon shows fan RPM and CPU temperature in the menubar together, so a spin-up that happens while you’re not looking gets caught. $14.99 lifetime. Download Beacon if you want to track this rather than guess.

The fan running constantly almost always traces to a single fixable cause. Finding it usually takes ten minutes.