Password screen
Enter the options screen, select "Game Status", highlight one of the characters, then press L + R.

Ultra rez option
Enter "GO_MAX_REZ" as a password. Note: This code requires the 4MB RAM expansion pak.

Invincibility
Enter "ELBICNIVNI" as a password.

All characters
Enter "LLA_KCOLNU" as a password to unlock all characters. Note: Their quests will not be completed.

All characters have maximum stats
Enter "LLA_DORTOH" as a password to upgrade all vehicles.

Rapid fire
Enter "RAPID_FIRE" as a password to remove the delay when shooting weapons.

Super missiles
Enter "BLAST_FIRE" as a password to increase the damage from missiles.
Faster cars
Enter "MORE_SPEED" as a password.

Heavier cars
Enter "GO_RAMMING" as a password to increase your car's weight and ramming ability.

Lighter cars
Enter "HI_CEILING" as a password to decrease your car's weight and hover higher than normal.

Fast action
Enter "QUICK_PLAY" as a password to enable a random fast action arcade feature.

Attract enemies
Enter "UNDER_FIRE" as a password to have three enemies attack simultaneously.

Slow-motion mode
Enter "GO_SLOW_MO" as a password.

No enemies in arcade mode
Enter "HOME_ALONE" as a password.

No gravity
Enter "NO_GRAVITY" as a password to reduce gravity to the point that your car will almost float when a bump is hit.

High suspensions
Enter "JACK_IT_UP" as a password.

Big wheels
Enter "GO_MONSTER" as a password.

No wheel attachment icons
Enter "DRIVE_ONLY" as a password to disable wheel attachment icons from spawning. -

View all ending sequences
Enter "LONG_MOVIE" as a password to view all endings in one continuous sequence.

Same cars in multi-player
Enter "MIXED_CARS" as a password to allow more than one person to select the same car in multi-player mode. -From: PinheadGun @ aol.com

Disable all codes
Enter "NO_CODE" as a password.