Why your USB device isn’t showing up on your MacBook and how you can fix it

USB wouldn’t be what it is today without Apple. The format predates the original iconic iMac — but Apple’s gumdrop-shaped computer helped popularize it by ditching all the legacy connectors that had been haunting the industry. USB became so commonplace, in fact, that the push came back to bite the company, with European Union regulations forcing it to ditch Lightning ports on iPhones. The days of Apple-exclusive ports are effectively over, MagSafe being the major remaining holdout.

Modern USB Mac accessories tend to be well-behaved. On occasion, though, macOS can fail to detect them, which is understandably maddening. With USB being as widespread as it is, anything less than a seamless experience feels unacceptable.

The good news is that there are known hardware and software explanations for why this happens, like damaged cords or an accessory that requires more power. In many situations the fixes are remarkably simple, particularly on the macOS side. There are rare instances, however, where you may need to seek outside help.

The first thing to remember is that by default, macOS requires you to give permission for accessories to connect. This prevents malware from being injected. At the same time, if you accidentally reject a permission prompt, a legitimate accessory won’t transmit data until you give the green light. Charging should still work in either direction.

Typically, you can force macOS to re-display the permission prompt by unplugging an accessory and plugging it back in again. To minimize future hassle, though, go to Apple menu > System Settings > Privacy & Security, then scroll down to the Accessories section. Here you can choose Ask for new accessories, Automatically allow when unlocked or Always allow. It’s best to skip that third option unless you’re always around your Mac or in a very secure environment.

If that doesn’t change anything, you might want to verify that macOS sees your device in the first place. Hold down the Option key, then click on Apple menu > System Information. If you see the accessory listed under Hardware, you may need to check the manufacturer’s online support info. If it’s invisible, or if it’s detected but you keep getting an error message when plugging in, there may be more we can help with.

A probable cause in that regard is power. Some accessories may require more than a Mac’s USB port can supply, in which case you should get a related message, and there may be a separate power cable you need to plug in. If there’s no separate power on your accessory, however, the USB port itself may be the issue. Try alternate ports on your Mac or connecting directly if you were using a hub or dock as an intermediary. If you keep getting power-related warnings, you may want to talk to Apple tech support — it could be that your Mac just isn’t feeding power to USB.

Speaking of hubs and docks, don’t forget that those often require their own power supplies. And even if they don’t, things can go wrong with device chains, since of course they have to successfully transmit power or data across multiple hops. We recently had an experience with a Thunderbolt dock in which a wireless mouse receiver became unusable until it was plugged directly into a laptop — never mind that an SSD on the dock was doing just fine. It’s always safer to skip the middleman if you have enough ports free.

Make sure that macOS is fully up-to-date by going to Apple menu > System Settings > General, then clicking on Software Update. Bugs or driver compatibility issues could hypothetically be interfering. Some accessories may also rely on proprietary software to do much of anything, in which case you’ll want to make sure the latest version of that is installed. Check the Mac App Store or a manufacturer’s website. External cards and drives need to use file system formats compatible with macOS, namely APFS, FAT or ExFAT. 

Lastly, be sure that you’re using the right type of USB cable for a device’s power and bandwidth requirements and that there’s no damage or debris interfering with either cables or ports. Things like lint and bent pins may be all it takes to block something from working. Lint, dust and grime can typically be cleaned out with an air can or by gently swiping a soft-tipped tool. As for damage, you’ll likely just need to swap in a new cable, especially if there are any signs of browning or exposed wires. Those signal a fire hazard.