To join the Modern Warfare multiplayer game, all you need to do is to press the A or X button on the second controller depending on what system (PS4 or Xbox One) you are on. Step 5. The second player will prompt to sign in to an Activision account to start playing the COD Modern Warfare split screen.

Clear the Cache of Your Console. Another common reason for the Call of Duty Modern Warfare Multiplayer not working error is the corrupted cache data. In this case, you can try clearing the cache files on your PC or console to fix the issue.