This thread started a long time ago but I just found a solution that worked for me.
1. Plug in an Ethernet cable and get Internet access.
2. Go to Device Manager -> Network adapters -> and double-click Intel(R) Centrino(R) Advanced-N 6230.
3. Click the Driver tab and uninstall the driver.
4. Go to Dell Support (dell.com/support/home) and jump through the hoops necessary for Dell to identify your computer model.
5. Go to Drivers and Downloads. Don't pay any attention to what Dell thinks you should download.
6. Find "Other ways to find drivers" and click "Browse all drivers for XPS 15Z L511Z".
7. Click Network and download Intel Centrino Wireless-N 1030/Advanced-N 6230 Driver (should be the first one on the list).
8. Click Run to allow the installation to proceed.
9. If the installation fails because you don't have the right .NET framework, allow it install the framework for you.
10. Repeat the Intel Centrino Wireless-N 1030/Advanced-N 6230 Driver installation. It should finish this time.
11. Download and run the Intel Centrino Wireless-N1030, 6230 Bluetooth 3.0+HS Application.
13. When the system comes back up, press Fn-F2.
14. Right-click the network icon in the notification area (you may need to enable it) and select Settings.
15. Set the Wi-Fi toggle switch at the top to On.
16. You should see a list of available wireless networks.