My MacBook Pro won't reconnect to my Wi-FI automatically after waking from sleep mode

Question

Hello, everyone. Since I updated to Yosemite, my MacBook Pro won't reconnect to my Wi-FI automatically after waking from sleep mode.
Does anyone know how to fix that?
Thanks in advance,
Arthur.

Answer 1

Hi, arthurpacifico. 
Thank you for visiting Apple Support Communities.
Here are a couple troubleshooting steps that I would recommend trying to see if it corrects this issue.
Intel-based Macs: Resetting the System Management Controller (SMC)
http://support.apple.com/kb/HT3964
Reset your computer’s PRAM
http://support.apple.com/kb/HT1379
If the issue persists, try the troubleshooting steps I have attached below.
Symptom: After restarting or waking from sleep, my computer might not connect to the Internet
After waking from sleep or starting up, your computer may not show that it is connected to a Wi-Fi network.
After start or wake, your computer may indicate that it is connected to a network, but does not connect to the Internet.
Solution
Use these steps if your computer does not automatically connect to your desired Wi-Fi network.
Check your TCP/IP settings in the Network pane of the System Preferences. Click the "Renew DHCP lease" button
Choose System Preferences from the Apple menu.
Choose Network from the View menu.
Select Wi-Fi, then click the Advanced button in the lower-left hand corner of the screen.
Click the TCP/IP tab from the top of the screen.
Click the "Renew DHCP lease" button.
Select the Wi-Fi tab and view your Preferred Networks list.
Select each network and click the minus sign to remove those networks from your Preferred Networks list.
Click OK and close the Network preferences.
Remove your stored network passwords using the Keychain Access Utility.Restart your computer.
Open Keychain Access from /Applications/Utilities. Your window will look like this:
Remove your AirPort network passwords from the login keychain: Select the "login" keychain from the Keychain sidebar. Click the "Kind" column to order the list of keychain items by their type. Remove all entries of the kind: "AirPort network password".
Remove your AirPort network passwords from the System keychain: Select the "System" keychain from the Keychain sidebar. Click the "Kind" column to order the list of keychain items by their type. Remove all entries of the kind: "AirPort network password".
Note: The above steps will remove your Wi-Fi network passwords. If you do not know them, or if your network does not use passwords to restrict access, you should contact your network administrator.
Join your Wi-Fi network. You will need to enter your password for your network again if it requires one.
Wi-Fi: How to troubleshoot Wi-Fi connectivity
http://support.apple.com/kb/ht4628
Cheers,
Jason H.