Under the secrets in options you can enter the codes listed below. They are dependent on a ''Secret Access Code'', different for each install of the game.
Password Effect
FNDDLF CODE GROUP: 33056 ALL CAR PARTS
TPDSTS CODE GROUP: 33056 ALL OTHER CARS
RLEVWG CODE GROUP: 33056 ALL TESTS
QMLRPI CODE GROUP: 33056 ALL TRACKS
SFKTCP CODE GROUP: 33056 EXPERT MODE
BEDMSH CODE GROUP: 33056 MIRROR TRACKS
MBNNOE CODE GROUP: 33056, GROUP B MODE/CARS
ZCDGEN CODE GROUP: 34674 ALL CAR PARTS
FEQRJV CODE GROUP: 34674 ALL OTHER CARS
WBDWYE CODE GROUP: 34674 ALL TESTS
ZCNGMW CODE GROUP: 34674 ALL TRACKS
IRZQNT CODE GROUP: 34674 EXPERT MODE
XOEFIP CODE GROUP: 34674 GROUP B MODE/CARS
HCHSFD CODE GROUP: 34674 MIRROR TRACKS
AJOOOU CODE GROUP: 62297 ALL CAR PARTS
AJOOOU CODE GROUP: 62297 ALL CAR PARTS
FNDKVA CODE GROUP: 62297 ALL OTHER CARS
FNDKVA CODE GROUP: 62297 ALL OTHER CARS
HFDHVM CODE GROUP: 62297 ALL TESTS
OHZJWH CODE GROUP: 62297 ALL TRACKS
OHZJWH CODE GROUP: 62297 ALL TRACKS
SPUFMB CODE GROUP: 62297 EXPERT MODE
SPUFMB CODE GROUP: 62297 EXPERT MODE
SMOJYN CODE GROUP: 62297 GROUP B MODE/CARS
SMOJYN CODE GROUP: 62297 GROUP B MODE/CARS
ABDLEO CODE GROUP: 62297 MIRROR TRACKS
UEDIUP CODE GROUP: 71077 ALL CAR PARTS
ZFBDKH CODE GROUP: 71077 ALL OTHER CARS
YCDYZH CODE GROUP: 71077 ALL TESTS
JJRGKX CODE GROUP: 71077 ALL TRACKS
ACDBEI CODE GROUP: 71077 EXPERT MODE
APCSTK CODE GROUP: 71077 GROUP B MODE/CARS
ZMDHKN CODE GROUP: 71077 MIRROR TRACKS
JUDFUE CODE GROUP: 76538 ALL CAR PARTS
EDDXVB CODE GROUP: 76538 ALL OTHER CARS
EUDNKA CODE GROUP: 76538 ALL TESTS
AHZSIX CODE GROUP: 76538 ALL TRACKS
CXYIYF CODE GROUP: 76538 EXPERT MODE
RTNITJ CODE GROUP: 76538 GROUP B MODE/CARS
VJFWEF CODE GROUP: 76538 MIRROR TRACKS
XKDBLU CODE GROUP: 84419 ALL CAR PARTS
EBDIQQ CODE GROUP: 84419 ALL OTHER CARS
CIDLCC CODE GROUP: 84419 ALL TESTS
SXDEBD CODE GROUP: 84419 ALL TRACKS
EIDYVP CODE GROUP: 84419 EXPERT MODE
EEHIZA CODE GROUP: 84419 GROUP B MODE/CARS
YUDWVP CODE GROUP: 84419 MIRROR TRACKS