Hi Florian.
Please try these steps to resolve your issue.
NOTE: These steps assume that the printer is powered on and connected to your network correctly, and are for network-connected printers only. If your printer is connected via a USB cable, then see the USB connection steps below.
1) Download the installation package from here.
2) Double-click the installation package named “Phaser_6140_OS_10.9_Print_Installer.dmg” from your list of downloads. Double-click the 6140 Print Installer package file.
3) Continue through the driver installation. When prompted, you’ll be required to agree to the Software License Agreement. You’ll also be prompted for the system administrator username and password.
4) Once the installation has completed, open your list of printers by going to System Preferences and double-clicking Printers & Scanners.
5) Click the + button to Add a Printer.
6) Allow the operating system a few moments to find the Xerox Phaser 6140 in the list of available printers. If it is not found after a few minutes, then skip down to Step 8.
7) Click the printer labeled Xerox Phaser 6140 from the list of printers automatically discovered. Ensure that the line labeled “Use:” is set to Xerox Phaser 6140 PS v3.1. Skip down to Step 11.
8) Select the IP category at the top of the Add menu.
9) Enter the TCP/IP IP address or hostname of the printer. Please see the article here if you need assistance determining your IP address.
10) In the “Name:” field, enter the name “Xerox Phaser 6140 PS.” Ensure that the “Use:” field has properly been set to “Xerox Phaser 6140 PS v3.1.
11) Click the Add button. Your printer should now appear in the list of available printers. You may print documents normally.
For printers using a USB connection, please use the following steps:
NOTE: These steps assume that the printer is powered off and disconnected from the computer.
1) Download installation package from here.
2) Double-click installation package named “Phaser_6140_OS_10.9_Print_Installer.dmg” from your list of downloads. Double-click the 6140 Print Installer package file.
3) Continue through the driver installation. When prompted, you’ll be required to agree to the Software License Agreement. You’ll also be prompted for the system administrator username and password.
4) Once the installation has completed, open your list of printers by going to System Preferences and double-clicking Printers & Scanners.
5) Ensure the printer is connected directly to the computer using a USB cable. USB Hubs, docking stations, and extender devices may still work, but are not supported and so functionality is not guaranteed. Power the printer on.
6) The USB connected printer should immediately appear in the Printers & Scanners list. You may print documents normally.
These steps were documented by Andrew in our Second Level Support.
As mentioned by Mitch in his earlier post, you may always call the Support Center for further assistance at 1-800-835-6100.
I hope this helps you.