Chosen Solution
I’ve got an issue on my iMac 27 mid 2011 (EMC2429). I can’t change the firmware password, nor disable it, and can’t permanently set startup sound volume. I know the password, I can run to recovery mode with typing the password, and when go to the ‘Firmware password‘ utility it says me it off (=has been disabled) while when I boot with ‘Option‘ or ‘Command+R‘ I’m still prompted for the password. I tried to disable it with ‘firmwarepasswd -delete‘, it says it is not set. The password does not hurt, but startup sound does, and it seems that one can’t run ‘Hardware Diagnostics‘ (Option+D) when firmware password is enabled. I found that PRAM battery replacement can help. Just did with the new BR2032. No effect, still system says that no password is set, while asking for password at recovery boot. Also did the full recovery re-install, with the partitions erasing, but no effect. Ideas?
Here’s the process to enable as well as disable: How to set a firmware password on your Mac
