I have a 2 GB SD card that I can't reformat. It seems pretty corrupted.

If I go into Disk Utility, I get these various error messages for each option:

  • Repair Disk:

    Disk Utility can’t repair this disk.

  • Erase (with Format "MS-DOS (FAT)"):

    Volume Erase failed with the error: Couldn’t modify partition map.

  • Set number of partitions to 1 and Apply:

    Partition failed with the error: Couldn’t open device.

According to Finder, I have permission to both read and write, and almost 100% of the space is available. However, if I try to copy any files on, I get an error message claiming there is not enough free space.

Any advice on how to fix this disk?

  • and after this you're going to trust any data to it, even if you can persuade it to format? Throw it away!
    – Tetsujin
    Commented Dec 20, 2015 at 10:13

7 Answers 7


Get drive name

diskutil list

then try

diskutil unmountDisk force /dev/DRIVENAME

Then format

diskutil eraseDisk JHFS+ Emptied /dev/DRIVENAME


diskutil eraseDisk FAT32 NEWNAME /dev/DRIVENAME
  • mad genius!!!!!
    – Shanimal
    Commented Sep 29, 2018 at 1:28
  • 12
    After the last step, error message: Error: -69877: Couldn't open device.
    – tvk
    Commented Apr 16, 2019 at 0:10
  • Error: -69760: Unable to write to the last block of the device Commented Jan 16, 2020 at 3:05
  • 3
    This worked to create some usable disk which then I could format again as MSDOS FAT using Disk Utility GUI
    – Vikram Rao
    Commented Jan 19, 2020 at 17:43

I had the same exact problem. Format your card using this application: https://www.sdcard.org/downloads/formatter_4/index.html

Worked perfect for me.


  • This program has brought my USB drives back from the dead. Amazing!
    – MikeSchem
    Commented Jun 19, 2018 at 18:48
  • Amazing indeed! Thank you very much, worked perfectly :))) Commented Jul 12, 2019 at 10:46
  • [ERROR] Invalid end of sector signature: 0x3B5A [ERROR] fat_check_validate_boot_sector returned error: 22 (Invalid argument) [ERROR] Initializing cached values failed: 22 (Invalid argument) [ERROR] Generated invalid volume. fat_volume_create returned: 22 (Invalid argument)
    – SimonS
    Commented Nov 23, 2021 at 18:35

Does it have a lock switch on the side? If the card is not corrupted, it could help to slide the lock switch several times.

  • I tried this -- it unfortunately did not help. Thank you though.
    – Bob
    Commented Dec 20, 2015 at 10:07
  • 2
    Those slides without markings are evil. Commented Mar 3, 2016 at 15:45
  • 1
    I had this problem, the sdcard adapter for microsd would move slightly when I plugged it into my sdcard reader. After some attempts moving it back and inserting it slowly I was able to make it work and then I could format the sd card. I experienced the issue in catalina
    – nck
    Commented Apr 16, 2020 at 16:02

I had the same issue on an iMac, Michelle mentioned using an external SD reader solved her problem so I figured it didn't make sense for it to be an OSX related problem. tried the tape, tinfoil and mid-position tricks to no avail. Some people go so far as to say there's a "light beam" inside the slot that reads the lock slider in the cards.

It came down to either buying a USB SD reader or opening the iMac to extract and service the reader part itself. Then I used a led light to see inside the slot itself and it was all in fact just pins. a pin is pushed when the card slider is in “lock” position preventing the OS from writing. I used tweezers to scrub inside the lock recess in the iMac slot, plugged the SD afterwards and it worked, it's writable again. might have been jammed with dirt and dust.

  • I used a folded over 20 dollar bill (any denomination should work of course!) and after stuffing it in & out a few times, voila! SD card was now writable! Thanks @zaiten
    – likethesky
    Commented Jul 29, 2019 at 3:00
  • I had the same issue. I was using the SD port in a 2015 15" macbook pro. It would give me the error. However, it did work using a USB SD card reader plugged into the same computer. Commented Dec 10, 2021 at 0:37

Not sure if anyone has put this as an option yet but, after fussing with this issue many times over, I brought out my dusty usb card reader and voila no more issues... Hope this helps...


I had the 'Disk Utility.app v15 (1511.3.1)' response "couldn't open device" on Mac OS X El Capitan 10.11.6, while trying to erase an external USB hard disk that had previously been used with Windows. After much struggling, what worked easily, was to boot into Rescue mode and use Disk Utility there🙄.

  • If you want to work on an external disk, plug it in
  • Restart -- or with the Mac shut down, start up -- while holding command-R until the progress bar under the Apple logo has progressed about 1/4 of the total distance
  • Choose 'Disk Utility' from the 'OS X Utilities' window
  • Chose the disk at the left, and click [Erase]
  • reboot into regular mode

If you feel comfortable with the terminal you can try using diskutil commands. (Make sure you have a current backup of your main hard drive and dismount all other drives, then insert the SD card.)

Read the man page for diskutil first.

Then make sure you are absolutely positive which disk is the SD card before you execute any command that could erase your hard drive if you are wrong.

You might read this post of someone with a similar problem: http://hints.macworld.com/article.php?story=20070306150736965

Good luck and be careful!

  • Thanks! I will try this as soon as I'm able to back up my main hd.
    – Bob
    Commented Dec 20, 2015 at 10:07

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