The Japan and European versions of the Toyota Prius are sold with an EV Button pre-installed by Toyota. For some reason, in the North American version this button is left off (note: speculation focuses on possible EPA/NHTSB regulations that were unclear as to whether the option to use 2 different 'fuels' was legal). Also it has been speculated that the decision came from Toyota, but no clear statement, at this writing, has come from Toyota.

However, the ECU is programmed for the EV button. Accessing this feature is in theory a simple procedure. One simply needs to plug a wire into the proper plug on the ECU, attach that wire and a ground wire to a momentary switch and EV mode is available.

Unfortunately, accessing the proper pin to plug the wire into the ECU plug, and threading the wire and ground are a bit tricky.

You may have read how on our 2004 Prius I just did the simple 'coastal tech' EV mod, but on the 2006 Prius I wanted something that looked totally factory so I used the actual Toyota EV button imported from Japan. The first step of the project was to order the EV switch, everyone on Prius Chat recommended Sigma Auto, the switch cost about $70 and took about a month to arrive but that is expected because it is ordered directly from Japan. For the wiring of the project I found some great tutorials on Prius Chat that pretty much walked me through the project, below is a link to the document I used for the project and a picture of the car post install.

Link to the factory EV button install instructions: factoryevinstall.pdf