Want to get any car (modded or not) from the singe player mode of GTA V into GTA Online? Then follow this guide - it works for both Xbox 360 and Playstation 3 versions of the game, and yes, allows you to bring full modded cars over from story mode to multiplayer!

Your spawn location must be set to "Last Location" and you should have no personal vehicles outside (they should all be in your garage). Go to the nearest Los Santos Customs and stand just outside. Then press pause, go to "Online" and select "Leave GTA Online". You'll spawn in story mode. Now you need to find the vehicle you want. If you want to mod the vehicle, switch to Franklin first and then once you have the vehicle you want, modify it at his LSC at Sandy Shores. Now, jump out of the vehicle and stand next to it, then press pause and start an invite-only session of GTA Online. You'll then spawn in GTA Online and should be across from the Los Santos Customs. Now find the nearest car (any) and take it inside the LSC. When inside, press pause and go the game store for your system. This is the important part: as the camera zooms out above the city, if you are on PS3 then press the PS button on your controller, go to PSN and press triangle over "Account Management". Sign out. If you are on Xbox 360, when the camera zooms out you need to unplug your network cable from your console. Either of the above methods will result in an error when your game store loads up and you will automatically go back to single player mode. When you're back in SP mode go back to the car you want to take over to GTA Online and take that to the nearest LSC. Drive up to the door of the LSC and when it opens park it halfway through (so that it can't close). Now stay in your car and if you're on PS3 sign back into PSN (and if on Xbox 360 plug your cable back in and sign in). Then press pause and start an invite-only session of GTA Online. You'll spawn in GTA Online and be near the LSC. Go to the LSC's door and you should find your car from story mode there parked under the door!

Extra tip for extra cash: What you should also notice is that a duplicate of the car is opposite the LSC. What you can then do is get the car across the street (leaving the first car under the LSC garage door) and drive it to just outside the LSC where the first car is. Then get in the first car and drive it into the LSC and sell it. Then you'll spawn outside with the "duped car" which will be your person vehicle and you'll have some GTA$!