To unlock all sub-missions for both the Autobots and Decepticons, insert the following code at the game’s main menu (where the campaign options are listed, et cetera): Left, Up, Right, Left, Down, Down.
Defeating Decepticons
Go to "The Suburbs" or "More Than Meets the Eye" levels. Go to the power plant. There is already a Decepticon there, but you can also bring one there. You will see some capsules marked "Danger, High Voltage". There are about 100 of them at the power plant. Pick up a capsule and throw it at the Decepticon. The capsule is highly explosive and causes quite a lot of damage. Make sure you are not caught in the explosion or you will be sent flying through the level. Also if you are closer to the city, this sometimes causes one or two police cars to come at you. There are a few of these capsules also at the junkyard. The same can be done with gas trucks in the junk yard or the gas tanks in the gas station near the junk yard.
Defeating Megatron
Megatron is the final opponent in the Autobots storyline. He will first be in his jet form and shoot two rounds at you. Use your shield to avoid them. After firing two rounds, he will land. His next attack is ramming. You cannot hit him while he is still focused on ramming. When he stops ramming and stands up in one place looking around, pick up any car and quickly throw it at him. If not done fast enough, he will return to ramming. If that happens, wait for him to stop again. If done successfully, he will now attack you. Hit him in close range combat with your melee attacks. After a few hits, he will return to being a jet. After two rounds of firing, he will again return to the ground. In his second attack, he will use his ball and chain. Throw another car at him. If done successfully, he will attack you again. Use melee attacks on him. He will then become a jet and fire at you again after a few hits. Do the same as before to avoid the attack. After firing at you, he will go back to the ground. His third attack is the flamethrower. Be careful because it will be difficult to get cars to throw at him. When he is hit by a car you threw, he will attack again. Use melee attacks on him. For the last time, he will become a jet again. Use the same strategy used earlier to avoid the attack. He will land after a few hits and attack you with all the attacks he used previously. Throw cars at him after each attack. After that, you will fight him for the final time. Use melee to defeat him.
Defeating the cement truck Decepticon
When you are fighting the cement truck Decepticon as Ironhide, transform and run him over to knock him down. Then, pick him up and throw him.
Defeating the Decepticon with a hose
During the mission when you are Ironhide and help Jazz at housing estate south, there is a Decepticon with a hose. You cannot hit him with melee attacks until you throw something at him. After that, you can pick him up, or when he gets up you can use melee attacks.
Floating water tower and other items
Play as Megatron and go to the place where the big dark green statue is located. Knock down the big tall brown pointy object. Take a water tower and throw it at the wall behind it. Pick it back up, then have Megatron face the screen like he is going to throw it at you. Just after it leaves his hands, pause game play. Resume the game and it will be floating. This might require a few attempts.
G1 Megatron
Collect all of the Decepticon Icons on all of the maps.
G1 Optimus Prime
Collect all of the Autobot Icons on all of the maps.
Infinite ammunition
At the menu with the "Campaign", "Bonus", and "Options" selections, press Up, Down, Left, Right, Up, Up, Down. If you entered the code correctly, the screen will flash.
Infinite health
At the menu with the "Campaign", "Bonus", and "Options" selections, press Left, Left, Up, Left, Right, Down, Right. If you entered the code correctly, the screen will flash.
No traffic, police, or military
At the menu with the "Campaign", "Bonus", and "Options" selections, press Right, Left, Right, Left, Right, Left, Right. If you entered the code correctly, the screen will flash. The only vehicles remaining will be parked.
Secret icon locations
Autobots
The Suburbs
1. The High School: On the roof of one of the High School buildings.
2. Bobby Bolivia's: Behind a building in the back of the used car lot.
3. The Mall: On the roof of the main building.
4. Sam’s House: Behind the billboard on the roof of building closest to Sam’s House. Drive down the street Sam's house is on towards the city. It is on the roof of the first building you approach.
5. Power Plant: On top of a fuel oil tank around the middle of the Power Plant.
More Than Meets the Eye
6. The Police Station: There is a ring of buildings around the central police station. The icon is behind middle building in this ring.
7. Power Plant: There is a park near the Power Plant. Look closely in the park to find it.
8. The Baseball Field: In the parking lot right next to the actual field.
9. The Police Station: In the alleyway of a square shaped cluster of buildings found on the street connecting the Police Station and the mall. It is on the right hand side of the street if going from the Police Station to the Mall.
10. The Baseball Field: On the roof of a building in the triangular shaped cluster of buildings between the Baseball Field and the Mall.
Inside Hoover Dam
11. Central Control Area: Inside the control room (progress through the story missions).
12. The Containment Lab: In front of Megatron (progress through the story missions).
13. Service Tunnels South C, D: In a corner to the right of the tunnel leading towards Service Tunnels South A, B area (close to the Chapter 1 dot on the mini-map, although on the opposite side of the wall).
14. Service Tunnels South C, D: Heading towards Service Tunnel North B, in a cubby hole on the left just before the road leading to the Central Core Area, above a health pick-up.
15. Service Tunnel North A: On the first level of the generator structure closest to the tunnel, on the side of the structure facing you as you come out of the tunnel.
The Last Stand
16. The Construction Site: Across the street on top of the tallest, tapering building.
17. Central Park: Near the bird statue.
18. City Boulevard West: Roof of tall, brick building near Chapter 3.
19. Central Park: Next to a water tower on top of a building across the street from the bird statue’s right wing tip.
20. Central Park: On the roof of the third cluster of buildings from Central Park directly behind the obelisk (from the starting point, go forward straight over the first two clusters of buildings. The icon is on top of the third set of buildings, a small one story building is to the right and a "Lush Dog's" billboard is to the left).
Decepticons
SOCCENT Military Base
1. U.S. Military Airbase: Next to the hangar near Chapter 1.
2. U.S. Military Airbase: Behind a building on the opposite side of the base from Chapter 1.
3. Supply Depot East: Near the tank lot (you can get it in the Attack sub-mission).
4. Bedouin Village: Near the center of the village.
5. Bedouin Village: Across the paved road from Bedouin is a cluster of small bases. The icon is next to the L-shaped base closest to the square base.
The Hunt for Sam Witwicky
6. High School: In the park next to the high school.
7. Bobby Bolivia’s: In the highway tunnel near the used car lot.
8. The Mall: In the middle of the three way alley in the cluster of buildings immediately between the Mall and the Baseball Field.
9. Housing Estate North: Between two houses on an elevated row of houses (first two house on left as you come up towards the dead end).
10. Sam’s House: Behind the brown house that is between two white houses. There is a health pick-up in front of the brown house.
A Gathering Force
11. The Tank Depot: Between two long buildings near the mountain.
12. The Recreation Area: Between two buildings on a curved part of the road (near the Baseball Field).
13. Roof of a building between the Recreation Area and the Aircraft Depot.
14. The Aircraft Depot: Behind a building that is near a fuel oil tank.
15. The Residential Quarters: In the middle of the larger housing circle.
City Of The Machines
16. Central Park: On top of the tall building facing the bird statue’s left wing.
17. Main Avenue: In a curved area with many umbrella covered tables.
18. Central Park: On the roof of the building cater-corner to the bird statue’s left wing.
19. Central Park: On the roof of the tall corner building in the cluster behind the bird statue.
20. Central Park: On the roof of the corner building cater-corner to the bird statue’s right wing.
Various Codes
Enter the following codes at the Campaign / Bonus Features / Credits menu:
Unlock Generation 1 Jazz Repaint - Left, Up, Down, Down, Left, Up, Right
Unlock Generation 1 Starscream Repaint - Right. Down, Left, Left, Down, Up, Up
Unlock Cybertron missions - Right, Up, Up, Down, Right, Left, Left
Unlock Robovision Optimus Prim - Down, Down, Up, Up, Right, Right, Right
Unlocks G1 Megatron - Down, Left, Left, Down, Right, Right, Up
Unlock All Mission - Down, Up, Left, Right, Right, Right, Up, Down
No vehicle's running on the street and no tank's/cop's attack - Right, Left, Right, Left, Right, Left, Right