Carmageddon Cheats - Full Game Only

In the scene where you choose to go to map select, vehicle select,
start race etc... type ENABLE(quickly) to be given access to all
tracks and vehicles. You can now use all of the other cheats in the
game...

First of all, when the race starts use F4 to cycle through the modes
untill CHEAT MODE appears. Then all the following cheats will become
availiable: 

F5 Total repair (free). 
F6 Toggle Invulnerability on/off. 
F7 Adds 30 seconds to the timer. 
F8 Freeze/Unfreeze timer 
F10 Increment lap counter 
F11 Earn 5000 credits instantly 
F12 Switch between each opponents camera and your own. External view
only. 

SHIFT-F6 Show opponents on map. 
SHIFT-F7 Adds 300 seconds to timer. 
SHIFT-F8 Toggle shadow between none/your car only/all cars. 
SHIFT-F10 Increment checkpoint counter 
SHIFT-F11 Lose 5000 credits instantly 

CTRL-F8 Toggle shadow between solid(faster)/translucent. 
CTRL-KEYPAD 1 Toggle fly mode
-Use normal movement keys. Keypad 5 places you on the ground(still
flying). Keypad 9 and 6 changes the cars pitch. 

Power-ups(still in cheat mode)

0 Bonus 
1 Mega bonus 
2 Pedestrians glued to ground. 
3 Giant pedestrians. 
4 Explosive pedestrians. 
5 Hot rod. 
6 Turbo pedestrians. 
7 Invulnerability. 
8 Free repairs. 
9 Instant repairs. 


SHIFT-0 Timer frozen. 
SHIFT-1 Underwater ability. 
SHIFT-2 Time bonus. 
SHIFT-3 Oh dear, body work trashed 
SHIFT-4 Blow yourself up 
SHIFT-5 Frozen opponents 
SHIFT-6 Frozen cops 
SHIFT-7 Turbo opponents 
SHIFT-8 Turbo cops 
SHIFT-9 Gravity has gone strange??? 

ALT-0 Pinball mode 
ALT-1 Wall climber 
ALT-2 Bouncey-Bouncey 
ALT-3 Oh dear, jelly suspension! 
ALT-4 Pedestrians shown on map. 
ALT-5 Pedestrian extro-bastard ray. 
ALT-6 Greased tyres 
ALT-7 Acme damage magnifier 

SHIFT-ALT-2 Instant handbrake 
SHIFT-ALT-4 Turbo! 
SHIFT-ALT-5 Mega-Turbo!! 
SHIFT-ALT-6 Blind pedestrians (to be used in conjunction with horn for a laugh) 
SHIFT-ALT-7 Pedestrian respawn 
SHIFT-ALT-8 5 free recovery vouchers. 
SHIFT-ALT-9 Solid granite car! 

CTRL-0 Rock springs! 
CTRL-1 Drugs! 
CTRL-2 Grip-o-matic tyres 
CTRL-3 Pedestrian Harvest 

(Quoted from a post by pcassidy@tecquip.co.uk)