Drive by wire is a technology that replaces traditional physical connections with a wire carrying an electronic signal. For example, on gasoline engines the throttle cable normally runs from the gas pedal to the butterfly in the throttle body that limits the amount of air going into the engine. As the gas pedal is pressed further down the butterfly opens wider, allowing more air into the engine. On fuel injected vehicles sensors detect the additional air and increased throttle position and instruct the fuel injectors to supply more fuel so that the engine starts to make more power.
With throttle by wire a sensor is attached to the gas pedal and detects how far it has been pressed. This information is then sent down an a wire to the car's computer. The computer analyzes the information and commands a motor to open the butterfly in the throttle body. Since the computer is in control of the throttle opening things like idle speed control, cruise control, and traction control can easily be integrated. Because automatic transmissions are also usually controlled by the computer it can adjust the throttle during gear changes. It also allows the addition of eco or sport buttons to change the way the throttle reacts when pressed, increasing fuel economy or throttle response.
Some vehicles also use a brake by wire system, often in conjunction with a normal braking system. The brake by wire system allows the vehicle to automatically apply the brakes based on events from the cruise control and collision mitigation systems. Steer by wire has been demonstrated on some prototype vehicles, and has also been used to steer the rear wheels on some vehicles. Shift by wire has replaced the traditional shift lever with buttons or knobs on many vehicles.
If for some reason your throttle becomes stuck open, it is important not to panic. The procedure is the same whether the car is equipped with a traditional throttle cable or throttle by wire. The first thing to do is to shift the car's transmission into neutral to prevent the engine from driving the wheels. The next step is to firmly apply the brakes and then slowly and carefully pull onto the shoulder, and bring the car to a controlled stop. If for some reason the engine still seems to be pulling the car forward turn off the engine by turn the key to the off position. Once the engine has stopped, immediately turn the key back to the On position (but don't start the engine) so that the steering doesn't lock. If your car is equipped with a Start/Stop button, press and hold the button until the engine shuts off. Be aware that with the engine off steering and braking effort may increase quite significantly. Once the car is safely on the side of the road do not attempt to drive it again until the throttle system has been fully checked.