NFS Undercover Codebreaker codes for PS2.
(All credit for these cheats goes to codetwink.com)

I'm not making any promises that all of these codes will work. I haven't turned all of them on. Some of them may crash your game and/or corrupt your savegame. Use at your own risk and have fun! (I recommend making a new savegame just for cheats, so that you don't risk losing everything.)
~SergeantCross8

Enable Code(Must be on)
905766E8 0C15D962
200A0000 3C010064
200A0004 8C217080
200A0008 1020001B
200A0010 8C210000
200A007C 03E00008
20576BBC 08028000

Max/Inf Money
200A0018 3C0205F5
200A001C 3442E0FF
200A0020 AC22004C

High Rank
200A0018 3C0205F5
200A001C 3442E0FF
200A0024 AC220050

Buying Parts Doesnt Decrease Cash
2060C298 24060000
2060C2B8 24060000

Buying Parts Increases Cash
2060C298 0220302D
2060C2B8 0220302D

Infinite NOS Usage
20416178 00000000

Freeze Timers
20459B2C 00000000

Infinite Speedbreaker
2045B6F8 00000000

Open All Parts/Cars/Races/Challenges**not saveable
00690594 00000001

Idiot Racer AI
20148E7C 1000000D

Disable Traffic & Cop AI
201376BC 10000011