The 16 inch MacBook Pro with the M3 chip has three Thunderbolt 4 USB-C ports, an HDMI port, an SDXC card slot and a MagSafe 3 port, and when a USB-C port seems dead the cause is usually the cable, debris or a software glitch. Asurion's guide and OS X Daily's guide agree on the order. Shine a flashlight into the port to look for lint, dust and damage, and clean it with a wooden toothpick or short bursts of air; pocket lint packs in over time.
The checks in more detail
Test the device on each port, and on another computer, to see whether the device or the port is at fault. Try a different cable, because a charge-only cable looks like a dead port, and Thunderbolt devices need a proper Thunderbolt cable. Restart the Mac, which refreshes the system and fixes many software glitches. Update macOS, since port faults have been addressed in updates. On Apple silicon there is no SMC reset to run; shutting down for thirty seconds does the equivalent. If a Thunderbolt dock or monitor does not appear, unplug it, restart and reconnect, with the dock's power connected first.
Check System Settings, Privacy and Security, Allow accessories to connect, which asks you to approve new USB and Thunderbolt accessories when the Mac is locked; a device blocked there does not work until you approve it. If only one port fails on every cable and device, the port may be damaged and needs Apple's service. A device that draws too much power, such as a bus-powered drive, may fail on one port and work on another because of power limits. Remember that the MagSafe port charges separately, and charging through USB-C uses a port.
If none of the ports work after a restart, contact Apple Support. If a bus-powered drive works on one port and not another, check that you are not exceeding the port's power budget: three Thunderbolt ports share power with the MagSafe charging, and a drive that draws a lot with a dock may fail when the Mac is on battery. Try powering the drive from its own supply or plugging the Mac in, and the drive often works. Note which ports you use for fast storage and which for slower devices.
Differential
Likely causes of “Apple MacBook Pro 16-inch USB or Thunderbolt device is not recognized”, and how to tell them apart
- 1
Lint or debris in the port
What separates it The plug is loose
How to confirm Clean it with a wooden toothpick
- 2
A charge-only or non-Thunderbolt cable
What separates it The device does not appear
How to confirm Use a data or Thunderbolt cable
- 3
An accessory not approved
What separates it The device is blocked
How to confirm Privacy and Security: Allow accessories to connect
- 4
A software glitch
What separates it A port stops responding
How to confirm Restart or shut down for thirty seconds
- 5
A damaged port
What separates it One port fails with every device
How to confirm Contact Apple Support
Before you touch a setting
Record this first — changing settings destroys the evidence
- Which ports fail
- Whether the device works on another computer
- The cable type
- The Allow accessories setting
Try in this order
0 of 6 completedLook into the port
ReversibleWith a flashlight.
Clean the port
ReversibleWooden toothpick or air.
Test the cable and device
ReversibleOn another computer.
Check Allow accessories to connect
ReversibleIn Privacy and Security.
Shut down for thirty seconds
ReversibleThen start.
Update macOS
ReversibleInstall updates.
Model-specific
What is true of this model and not of its siblings
- Thunderbolt 4
- Three ports on the 16 inch Pro.
- Security setting
- New accessories may need approval.
Stop boundary
When this stops being a self-service repair
- !If every port fails after a shutdown, contact Apple Support
- !If one port is loose, it needs repair
- !If a dock fails, ask its maker
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why does my MacBook Pro USB-C port not work?+
Debris, a cable or a setting.
Is there an SMC reset?+
No, shut down instead.
What is Allow accessories to connect?+
A security setting.
How many Thunderbolt ports does it have?+
Three.