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First you should make sure that you have the latest driver installed for you MX340
Download the latest driver from:
On the above website click downloads
Then select software
and then select the operating system that you currently are using on your mac
Also under the download section of the above website you can download the canon pixma wireless setup tool to assist in making sure the printer is connected properly
If the above does not assist in correcting the issue do the following steps
Open Printer & Fax under the Hardware section of System Preferences
Double click on the MX340 printer and you will get the option to 'Set default printer' and "Restore printer system".
Choose "Restore printer system".
Please Note: This will remove all printers from your printer list
Then click Add (+) to add a new printer.
Choose the printer, change the name (if you would like to) and select add.
After that the printer should start working as expected
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