Any gamer knows that there are certain combinations of key presses that unlock special features in games - invulnerability, or unlimited ammunition, or making your badass battle tank armed to the teeth with every weapon in the game look like the Oscar Mayer weinermobile. Though perhaps not quite as powerful as they are in games, cheat codes also exist in today's highly computerized cars.
For instance, it's a little kept secret among Toyobaru owners that the REAL way to disable traction and stability control for racing is NOT pushing and holding the traction control button for five seconds. That way is good enough for normal drivers, but it still leaves a little bit of traction control enabled to help the Torsen differential perform its limited slip functions, which is unacceptable for real drivers. The real way to turn off traction control is to fully warm up the car, and then within the first 30 seconds after turning it on, push BRAKE BRAKE BRAKE (hold the pedal down), HANDBRAKE HANDBRAKE HANDBRAKE (hold the lever up), BRAKE BRAKE BRAKE (hold the pedal down), HANDBRAKE HANDBRAKE. The usual dashboard lights indicating the traction and stability control are fully disabled light up, but now there is absolutely no electronic assistance whatsoever. The standard buttons can't deactivate this mode, either - only turning off the car will stop this madness. Following this procedure is the FR-S/GT86/BRZ's way of playing this scene from Blazing Saddles.
This is just one example from one car. What other automotive easter eggs are out there?