Every Toyota Prius that rolls off of the assembly line has the programming built into the computer to enable “EV” (”electric vehicle”) Mode. EV Mode tells the computer controlling the Prius to turn off the gas engine and use only its batteries until one of the following things happens:
- the batteries get too discharged (down to 2 bars on the Prius’ Energy display)
- the vehicle speed hits 35mph
- the driver asks for a lot of power (climbing a steep hill or getting onto the highway)
- the drive disengages EV Mode
When one of the above conditions is met the gasoline engine will turn on and the Prius will be out of EV Mode and back into its normal driving mode.
Because of reasons no one quite understands the Prius that you buy in the United States is missing the button on the dashboard to initiate EV Mode (but we all know that it’s somehow because of lawyers, right?). The computer in the US-market Prius knows what EV mode is and what it’s supposed to do when it’s in EV Mode — it’s just that there’s no way to tell the it that you want it to engage EV Mode. Unless you hack your Prius a bit.