Mac 10.10.5 suddenly can't scan with hp scan. doesn't see as scanner, but can print.

[mogardner]

Suddenly cannot scan, but can print

[BryanCustomPure]

Try this set/order below to get up and running again:

Use the HP Uninstaller: https://support.hp.com/us-en/document/c02440673
If you still have a folder marked HP, delete it (likely here: /Library/Printers/hp ).

Use Easy Start ( https://support.hp.com/us-en/drivers/selfservice/hp-easy-start/7376041      -make sure your OS is correct)

and see if your printer is supported. If not, or this doesn't solve the issue,  move on to the next steps.

Uninstall your printer USING THIS METHOD ONLY (NOT EASY START, NOT EASY ADMIN): Apple Logo (Upper Left of Screen)/System Preferences/Printers & Scanners. Then restart your computer.

See if you can print. If not, continue:
Download (and install) this package (From HP FTP) which will update drivers AND THE CERTIFICATE:
ftp://ftp.hp.com/pub/softlib/software12/HP_Quick_Start/osx/Installations/Essentials/hp-printer-essen...  
If the link comes up blank, try right/control clicking and saving it. Or right/control click and copy link, and paste into browser bar. If you get the malware warning part-way through the installation, go to System Preferences>Security & Privacy where you can tick a box and unblock the HP option.

The install takes a bit. Let it run, even if it seems like it stalled out! When it completes, restart.

Then reinstall your printer using: Apple Logo (Upper Left of Screen)/System Preferences/Printers & Scanners, and use the default drivers. If drivers do not show up, download and install the 5.1 driver package from here: https://support.apple.com/kb/dl1888?locale=en_US . Then restart your computer.