In recent years, with the popularity of digital devices, people are increasingly using SD cards to store and transfer data. However, sometimes we come across a common problem that the SD card is not recognized when we are using a Mac computer. This brings a lot of trouble to our usage, especially when we urgently need to get back the data from the SD card. So, how do you fix this?
First of all, you need to make sure that your SD card is properly connected to your Mac computer. If you are using the built-in SD card slot, then make sure that the SD card is inserted and not loose. If you are using a USB card reader, then check that the card reader is plugged into the USB port of your Mac computer and is not loose. Sometimes, restarting your computer will fix some problems. Once you have tried to restart your Mac computer, insert the SD card again and see if it is recognized. If you still can't recognize it, you can try the next step. Sometimes, the SD card may only be a temporary connection issue, you can try to unplug it and insert it again to see if it can be recognized by your Mac computer. 
If none of the above methods work, then the last solution is to restore its ability to read your Mac computer by reformat your SD card. However, doing so will erase all the data in the SD card, so be sure to back up your data before doing so. If you are familiar with terminal commands, you can also use Terminal to reformat the SD card. Open the terminal, run the command "diskutil list" to see the device identifier of the SD card, and then run the command "diskutil erasedisk file system."name/dev/identifierto reformat the SD card.
All in all, when your Mac computer can't read your SD card, there are several ways to try to fix this problem. First of all, using Disk Utility to unlock your SD card may be the easiest way, but it may also be ineffective. At this point, you can try to use Renee data recovery software to fix the SD card unreadable issue. Finally, if none of the above methods work, you may need to reformat your SD card to restore your Mac's ability to read it.