It's most possible that an incompatible or corrupted file system stops your Mac from reading the SD card. Besides, a damaged USB port, SD card with the write protection on, and other factors can also cause the SD card not reading on Mac.
Here, I'll explain each reason in detail to help you have a better understanding of why is Mac not reading SD card.
- The USB port is physically damaged for some reason. In case you are using an SD card adapter to connect your memory card to the Mac, when you connect it to a damaged or faulty Mac USB port, the Mac won't connect to the memory card. Not to mention to read it.
- The SD card is write-protected and can't be accessed. You may not notice but there's actually a slider on one side of your SD card. By pushing the slider up and down, you can enable and disable the SD card write protection.
- Faulty SD card reader. MacBooks coming out these years are not equipped with an SD card slot, therefore, an SD card reader is required for Mac users. However, if the card readers are misfunctioning or not recognized by the Mac, your Mac won't read the SD card.
- The memory card has an incompatible file system with the macOS. Although most SD cards are formatted in exFAT or FAT32, it's possible your memory card is having a format that's not working on Mac, say, an NTFS format.
- The SD card is physically corrupted. While the memory card is easy to carry, it's also vulnerable to physical damage. A simple break can cause your SD card to not work normally.
- There are some logical errors with the SD card. Perhaps the memory card is having some system issues, for example, the file system is corrupted and needs to be repaired for use. In this case, you can try repairing the card in Disk Utility.
Besides, an outdated reader driver can also cause your SD card not to read on Mac. You may check these reasons one by one to find out the true culprit.