Monster trucks are not available in Grand Theft Auto 4. As such, there are no cheat codes involving monster trucks. However, there are mods that add monster trucks to the game and some cheat codes interact with them.
Players on PCs can download modifications to add monster trucks to the game. GTA4-Mods.com has several free monster truck mods. Players can download these mods without signing up for an account on the website.
While in a monster truck, using the full health and armor cheat can also repair the vehicle. Press the up key on your keyboard to bring up the phone and dial 3625550100 to activate the cheat code. Note that using this cheat disables several achievements on Steam.