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Prius EV Mode Button

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Enabling the EV-mode Button, The missing secret missing feature.

The EV-Mode Button is a standard part of the Japan and EU Prius but was not installed in the US versions, perhaps because of extended warranties in Ca due to AT-PZEV regulations and qualifications criteria. The US Prius is still entirely aware of the EV-Mode though it can never get the signal or command to enter or exit the mode because a wire, light and button are missing. EV-Mode is a very enlightening feature as it encourages the Prius to stay in its electric mode for far longer than it normally would. It will normally drive 1 to 2 miles and up to 3 miles on a fully charged battery, after which it must restart the engine and use gasoline to recharge the battery. It is not a good idea to fully cycle the battery often as this decreases any battery's life and is not helpful for mileage if used improperly. If used correctly is can be advantagious for times when you know you won't need to start the engine. It's also fun for showing off and offers a small glimpse of the potential of electric vehicles.

The ev-mode function itself is activated and deactivated by grounding the H14 #27 pin on the HV ECU located behind the glove box(s). (ph) has a well integrated 3-wire EV-Button kit with easy instructions or prius-evbutton-install.pdf from and EV-button-Y.html from have more information for "do it yourself" kind of people like me. I also found a factoryEV.pdf by ScubaX at PriusChat which I had hoped would lead to the ev-status illumination solution, but instead simply found that the dimmer switch white/black stripe wire to be ground(-) and the grey wire to be illumination control. I'm looking for the steering pad wire diagram as I'd like to use the recirculation button as the ev-button, but it's probably not a simple ground.

Things you need to add the feature.

  • 22 gauge wire, about 6 feet.
  • Standard Philips screwdriver.
  • Small Jewler's screwdriver.
  • Soldering may be required.
  • 1/2 to 3 hours of time.
  • optional components:
    • momentary switch, batteries, drop cord?