fullgarage - Unlock all of the vehicles (Enter in garage)
wantstreets - Unlock all of tracks (Enter in menu)
adac - Repair car (Works in campaign,race,and splitscreen)
useshell - No damage (Works in campaign,race,and splitscreen)
needspeed - Endless boost (Works in campaign,race,and splitscreen)
goaway - All spawned traffic explodes
wannago - No respawn when going outside the track (Free Ride).
Just type any cheat codes while race,or also in pause

Unfotunately all of the cheats doesnt work in multiplayer,however,if you want at least some free roam mode in mp,just choose Checkpoint race,and enjoy
In Singleplayer,i recommend you to enable wannago cheat in racing