Accessing Cheat Mode
So many people have asked the question, so here’s the answer..

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 may prevent achievements from being earned.

Cheats you can do on your PS3

1. Weapons #1: R1, L2, R2, L1, Up, Down, Left, Right, Up
2. Weapons #2: R1, L2, R2, L1, Right, Down, Left, Up, Right, Down, Left, Up
3. Weapons #3: R1, L2, R2, L1, Right, Down, Left, Up, Right, Down, Left, Up, Right, Right
4. Faster Running Speed: R1, R1, Left, Right, L2, Square, Triangle, L1, Circle
5. Invincibility: R1, Circle, Circle, L2, R2, Triangle, X, L1, Right
6. Health: R1, L1, L2, Square, R2, Left, Right, Left, Right
7. Money: Press Up, Down, L1, L2, Left, Right, R1, R2, Square

Full health, armor, and ammunition
Dial “4825550100” into the cell phone.

Note: This phone number translates to “GTA-555-0100″. This code prevents the “Cleaned The Mean Streets” achievement from being earned.

Map Locations
Enter “www.whattheydonotwantyoutoknow.com” into the in-game computers to view maps that reveal all weapon, health, armor, vehicle, pigeon, ramp/stunt, and entertainment locations.

While playing the game, enter one of the following codes by dialing them into Niko’s cellphone to activate the corresponding cheat function. Note: Enabling some cheats may prevent achievements from being earned.

Refill health
Dial “3625550100″ into the cellphone. Note: This prevents the “Cleaned The Mean Streets” achievement from being earned.

Refill health and ammunition
Dial “4825550100″ into the cellphone. Note: This prevents the “Cleaned The Mean Streets” achievement from being earned.

Weapons tier 1
Dial “4865550100″ into the cellphone. This will unlock the baseball bat, handgun, shotgun, MP5, M4, sniper rifle, RPG, and grenades. Note: This prevents the “Cleaned The Mean Streets” achievement from being earned.

Weapons tier 2
Dial “4865550150″ into the cellphone. This will unlock the knife, Molotov cocktails, handgun, shotgun, Uzi, AK47, sniper rifle, and RPG. Note: This prevents the “Cleaned The Mean Streets” achievement from being earned.

Remove Niko’s wanted level
Dial “2675550100″ into the cellphone. Note: This prevents the “Walk Free” achievement from being earned.

Add one star to Niko’s wanted level
Dial “2675550150″ into the cellphone.

Spawn Annihilator
Dial “3595550100″ into the cellphone. Note: This prevents the “Walk Free” achievement from being earned.

Spawn Cognoscenti
Dial “2275550142″ into the cellphone.

Spawn Comet
Dial “2275550175″ into the cellphone.

Spawn FBI Buffalo
Dial “2275550100″ into the cellphone.

Spawn Jetmax
Dial “9385550100″ into the cellphone.

Spawn NRG-900
Dial “6255550100″ into the cellphone.

Spawn Sanchez
Dial “6255550150″ into the cellphone.

Spawn SuperGT
Dial “2275550168″ into the cellphone.

Spawn Turismo
Dial “2275550147″ into the cellphone.

Change weather and brightness
Dial “4685550100″ into the cellphone.

Easy money
Go to an ATM, then cause a traffic jam to the area. Wait for someone to take money from the ATM, then kill him or her. Make sure to block any nearby roads so the ambulance cannot get to the murdered victim. Take the money they dropped on the ground. Then, run a short distance away, and go back. The money should have respawned on the ground. You can repeat this as many times as desired. You can also kill more people taking their money from the ATM to increase the amount of money that respawns. -From: Khairol161

Repair engine
If the vehicle you are driving breaks down and the engine will not start, call 911, and your engine should start again.

Avoiding toll booths
Drive through any toll booth with any emergency vehicle with the sirens on. The booth attendant will open the gate, and you will save $5.