The Online Pass IS required to play online.Select Multiplayer from the main menu then Xbox Live. (The game will now connect you to the dirt servers)
Now select
Jam Session you can either search for a game an hope you find an unstarted game or host your own, as its a Jam Session you
can boost this with friends or other players.
Note Joyride sessions last 20 minutes so a race in progress could take a while to finishThe achievement will unlock at the end of the game,
the other 3 players Do not need to remain in the game throughout, Thanks Riksta10001 for confirming. It seems a patch of some sort may have been applied that has made it so all players need to remain in the game.Here's a link to
create a gaming session.