Unable to scan

Solve scanning problems on Mac - Apple Support

More information would elicit more help. Describe your particular model scanner, how it's connected to your Mac, the apps you're using to scan... etc.

Writing an effective Apple Support Communities question - Apple Community

sgegbg Said:

"Unable to scan: Hi, my printer says idle when I attempt to scan but not when I print from my Mac or the printer."

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Updating the Drivers:

You may need to install new drivers, if you have upgraded to a new macOS. You would:

1. Backup: the Mac*
2. Remove: the printer (System Preferences > Printers & Scanners > Select: the printer > Press: "-" button)
3. Restart: the Mac
4. Add: the Printer with New Drivers**

*First, Back up your Mac:

Create a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the upgrade.

**Go Here: Add a printer on Mac - Apple Support

sgegbg Said:

"Unable to scan: I have a 'vintage Mac air' so not able to upgrade to the latest iOS. I don’t use an app to scan. Until yesterday I opened the Printer from Systems, selected my printer and then selected scan. Put the item I wanted to scan in the printer and selected scan to file. No problems until yesterday. Why new printer drivers if I am still able to wirelessly print from my Mac without issue?"

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Can you scan with other devices that what you mention? If not, it may be the printer itself. Please provide the model of the printer, along with the model of your MacBook Air? If needle, contact the manufacturer.

To troubleshoot in depth, perform the following, in the order provided:

I. Use MalwareBytes for Mac:

This is software that searches for malware/adware. So, scan with it and then remove what is found. Once removed, uninstall MalwareBytes for Mac. Then restart the Mac. It is created by longtime users of these forums. So, that is why it is the only way to go about securing your Mac, when it comes through use of software 

Downloads:

1. Malwarebytes Anti-Malware for Mac
2. Malwarebytes uninstaller

II. Reset the SMC and NVRAM:

Sometimes changes are made to the system and then settings (i.e. for Safari) become manipulated, technically.  So, reset both on your Mac. It might take up to three tries to successfully reset these. To be certain you have the time to perform these.

III. Any Security Software Installed?:

Security Software's firewall settings would want to make sure that you are getting secure accessibility to your Mac. So, connecting items would not be a possibility, if firewall settings are part of it and enabled. So, uninstall it, using the uninstaller from the developer’s site. Just dragging a dropping its icon into the Trash will undesirably leave caches and other files sitting around on your Mac. So, to get the correct uninstaller, contacting the developer of the SecuritySoftware.

IV. Create a New Administrator User:

Are you logged in as an Administrator? Create a new Administrator user, and see if this still occurs while you are logged into a different Administrator user. If not, then it is something configured in your current user. So, from there, delete the current user and then just use this new administrator account. You would move all of your files over to it. See if that fixes it.