Grand Theft Auto IV Cheats

While playing the game, press Up to display Niko's cell phone. Press Up again to access the keypad. Then, enter one of the following codes to activate the corresponding cheat function. Once a code has been entered correctly, a new "Cheats" menu option will be available on your phone, below "Options", where you can access the cheats without having to enter the phone number again. Note: Do not save the game after enabling a code to avoid unforeseen problems. Enabling some cheats will prevent the indicated achievement(s) from being earned. You can usually only spawn one vehicle at a time. Any previously spawned vehicles will disappear. However, if you spawn a vehicle, save the game, and load again, you can spawn another one and your original will not disappear. You must have it in your parking space in front of a safehouse or it will be gone before you have a chance to spawn another.

Full health and armor

Dial "3625550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "DOC-555-0100". This code prevents the "Cleaned The Mean Streets", "Finish Him", "One Man Army", and "Walk Free" achievements from being earned.
Full health, armor, and ammunition

Dial "4825550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "GTA-555-0100". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Weapons tier 1

Dial "4865550100" on the cell phone. This will unlock the baseball bat, handgun, shotgun, MP5, M4, sniper rifle, RPG, and grenades. Note: This phone number translates to "GUN-555-0150". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Weapons tier 2

Dial "4865550150" on the cell phone. This will unlock the knife, Molotov cocktails, handgun, shotgun, Uzi, AK47, sniper rifle, and RPG. Note: This phone number translates to "GUN-555-0100". This code prevents the "Cleaned The Mean Streets" achievement from being earned.
Remove Niko's wanted level

Dial "2675550100" on the cell phone. Note: This phone number translates to "COP-555-0100". This code prevents the "One Man Army" and "Walk Free" achievements from being earned.
Add one star to Niko's wanted level

Dial "2675550150" on the cell phone. Note: This phone number translates to "COP-555-0150".
Spawn... 

To get 100% you have to complete the following:

* Complete all Main Missions.
* Complete all 10 Drug Deliveries.
* Complete all 10 Races.
* Complete all 10 Assassination missions.
* Complete all 30 car thefts.
* Collect all 10 cars for the Exotic Exports mission.
* Unlock all five friend's special abilities and complete the activities with Little Jacob, Brucie and Packie.
* Beat the computer or an online friend in all activities.
* Find all Random Characters and complete their missions (except for Jeff, Cherise, Clarence & Ivan).
* Complete all 30 Most Wanted Missions.
* Complete all 20 Vigilante Missions.
* Kill all 200 Pigeons.
* Complete all 50 Unique Jumps.

At the start of the game drive north to Bohan, the island where you get a safehouse after your first one is burned down. At the very northern most road there is a point where the subway train tracks go from an elevated line to underground. Drive a car from the road onto the tracks and head into the tunnel. Eventually you'll cross the river and end up on the locked island of Algonquin and receive 6 stars. Stay in the tunnel for 5 minutes and you'll get the achievement.

Reach the indicated level of friendship with the corresponding character to unlock their special friendship ability:

Alex (screen name "LiberatedWoman")

Method: Look for the personal ad from "LiberatedWoman" in the "Women seeking men" section of the "www.craplist.net" website. Alex is somewhat of a self-centered, spoiled rotten rich girl. She will compliment Niko for wearing expensive clothing and driving expensive cars. She will also write about her exploits with Niko in her blog at "www.blogsnobs.org". Reach 80% friendship with her.

Special ability: 50% off at all clothing stores.

Brucie

Method: Take him bowling, drinking, eating, strip clubs, shows, helicopter tours, and boating to reach 70% friendship.

Special ability (Chopper Ride): Call Brucie, and he will fly his helicopter to you. This allows you to fast travel to various portions of the city.

Carmen (screen name "SoboHoe")

Special ability (Health Boost): Restores Niko's health over the phone. She will call Niko every chance she gets.

Dwayne

Method: Take him to strip clubs, eating, drinking, shows, and bowling to reach 60% friendship.

Special ability (Extra Help): Call Dwayne to have a car full of gang members follow you.

Kiki (screen name "LawChick")

Method: Date LawChick via "www.love-meet.net" through the in-game internet. Take her out a few times to reach 75% friendship. When dropping her off, select the "Try your luck" option. Afterwards, she will call you and say she can clear the feds.

Special ability (Remove Up to 3 Wanted Stars): Call her on your cell phone, and select "Clear wanted levels".

Little Jacob

Method: Take him to darts, shows, pool, drinking, eating, and strip clubs to reach 60% friendship.

Special ability (Discount Guns): Call Little Jacob, and he will drive out a car full of guns for you to buy.

Packie

Method: Take him to strip clubs, shows, darts, drinking, bowling, pool to reach 75% friendship.

Special ability (Boom?): Call Packie, and he will make a car bomb for you.

Roman

Method: Take him to bowling, darts, drinking, eating, pool, shows, and the strip club to reach 60% friendship.

Special ability (Free Ride): Call Roman, and he will send a free cab.

Stevie

Method: Successfully complete all 30 of his vehicle thefts.

Special ability: The South Bohan garage will now offer money for any... 

Off The Boat (5) -- Complete the first mission.

One Hundred And Eighty (10) -- In a darts game score 180 with 3 darts.

Pool Shark (10) -- Beat a friend at pool.

King of QUB3D (15) -- Beat the High Score in QUB3D.

Finish Him (15) -- Complete 10 melee counters in 4 minutes.

Genetically Superior (25) -- Come first in 20 singleplayer street races.

Wheelie Rider (30) -- Do a wheelie lasting at least 500 feet on a motorbike.

Gobble Gobble (10) -- Score 3 strikes in a row, a turkey, in 10-pin bowling.

Driving Mr. Bellic (10) -- Unlock the special ability of taxi.

Rolled Over (30) -- Do 5 car rolls in a row from one crash.

Walk Free (50) -- Lose a 4 star wanted rating by outrunning the cops.

Courier Service (10) -- Complete all 10 package delivery jobs.

Retail Therapy (10) -- Unlock the special ability of buying guns from a friend.

Chain Reaction (20) -- You must blow up 10 vehicles in 10 seconds.

One Man Army (40) -- Survive 5 minutes on 6 star wanted level.

Lowest Point (5) -- Complete mission "Roman's Sorrow".

Order Fulfilled (10) -- Complete all 10 Exotic Export orders.

Manhunt (15) -- Complete the most wanted side missions from the police computer.

Cleaned The Mean Streets (20) -- Capture 20 criminals through the police computer.

Fed The Fish (5) -- Complete the mission "Uncle Vlad".

It'll Cost Ya (5) -- Complete a taxi ride without skipping from one island to another.

Sightseer (5) -- Fly on all helicopter tours of Liberty City.

Warm Coffee (5) -- Successfully date a girl to be invited into her house.

That's How We Roll! (10) -- Unlock the special ability of helicopter.

Half Million (55) -- Reach a balance of $500,000.

Impossible Trinity (10) -- Complete mission "Museum Piece".

Full Exploration (20) -- Unlock all the islands.

You Got The Message (20) -- Deliver all 30 cars ordered through text message.

Dare Devil (30) -- Complete 100% of the unique stunt jumps.

Assassin's Greed (20) -- Complete all 9 assassin missions.

Endangered Species (50) -- Collect every hidden package in the game.

Under The Radar (40) -- Fly underneath the main bridges in the game that cross water with a helicopter.

Dial B For Bomb (10) -- Unlock the special ability of phoning for a bomb to be placed.

Gracefully Taken (10) -- Complete mission "I'll Take Her".

Liberty City (5) (20) -- After meeting all possible friends, the ones left alive...