Unlock All Cars:
To unlock all cars, enter the following cheat using the D-pad on the Title screen:- U, U, D, A, A, RT, B, B, D.Press the Y or R button to choose the course or mode (ie. SS1, SS2, SS3), some of the details will be simplified. Also, the clock timer will move to the right side of the screen.
Finish first in all 10 years of the Championship mode and you will be able to race in a Secret Rally course.

Access hidden Sega Rally cars:
Renault Maxi Megane: finish Arcade Mode
Subaru Impreza 555: finish 1st (1st Year Regular Mode)

Mitsubishi Lancer EVO 4: finish 1st (2nd Year Regular Mode)

Toyota Celica GT-Four ST-185: finish 1st (3rd Year Regular Mode)

Mitsubishi Lancer EVO 3: finish 1st (4th Year Regular Mode)

Peugeot 106 Maxi: finish 1st (5th Year Regular Mode)

Lancia Delta Integrale: finish 1st (6th Year Regular Mode)

Fiat 131 Abarth: finish 1st (7th Year Regular Mode)

Peugeot 205 Turbo: finish 1st (8th Year Regular Mode)

Renault Alpine A110: finish 1st (9th Year Regular Mode)

LANCIA 037 Rally: finish 1st (10th Year Regular Mode)

Pressing L while selecting the year you want to race (1, 2, 3, etc.) will make the year a bit easier by adding extra time to your timer.
By pressing L while selecting the Corolla WRC, Lancer Evolution V, or Lancia Stratos you are giving a different paint job for your car. The alternate paint jobs are shown below; original on the left, different on the right.

At the title screen press; up, left, down, right, B, A, B, right, down. This enables all tracks in the 10-year championship, even the secret track.

Hidden cone challenge:
Select arcade mode and begin game play in the Rivera race in either championship or practice. Drive as usual until reaching the last turn. Two red construction cones should appear as the turn is approached. Intentionally hit both of the cones. A sound with each hit will confirm this part of the trick. Turn around, and drive your car in the wrong direction. An opening to a hidden section of the track will eventually appear. Enter it to find a hidden section of track that contains many construction cones. The game will give you 29 seconds (separate from the normal race time) to knock down as many cones as possible for 100 points each.