The Plug-in Prius “EV” Button is Missing in Action

By · February 24, 2011

BYD F3DM EV Button

BYD offers an EV button on the F3DM plug-in hybrid. The prototype version of the Prius Plug-in Hybrid do not.

Last week, I had the chance to use a prototype version of the Toyota Prius Plug-in Hybrid for my daily driving for three days. Even though the dashboard MPG was maxed out to 99.9 mpg for most of that time—spent running short-range trips around Berkeley—the Prius-with-plug felt slightly dissatisfying to me.

The pang of disappointment had nothing to do with relatively small battery pack (compared to other plug-in hybrids). It provided about 11 miles of mostly electric range—enough for all my driving for those days except for a single trip from Berkeley to San Francisco. It was the fact that the Prius PHV prototype lacks an “EV” button. That button would allow drivers to absolutely keep the gas engine off when they know it's not necessary.

Electricity Is Addictive

Last May, during my previous drive in the Prius Plug-in Hybrid, I was impressed with how often the car stayed in EV mode. On that 18-mile test drive, I was in EV mode for 14 miles, and tallied 87.7 MPG. So, why am I less impressed now? Because since that time, I’ve had several trips in other plug-in hybrids: a few times behind the wheel of the Chevy Volt and one full day in the BYD F3DM Chinese production model.

In the case of the Chevy Volt, there’s no EV button per se. Instead, the technical design keeps the engine off during the first 35 to 40 miles. This means no engine noise, no burning of gas, and no tailpipe emissions during those miles. In the case of the BYD F3DM, drivers can punch the EV button to achieve the same no-gas driving for about the first 30 miles. BYD’s plug-in hybrid provides the option to switch into hybrid “HEV” mode—but that wouldn’t get much use for my daily driving. Why run the gas engine unless you really need to?

For both Volt and F3DM (in EV mode), it doesn’t matter how hard you jam the accelerator pedal, it’s all smooth, swift and silent electric driving. That’s mostly but not entirely true for the Prius Plug-in Hybrid. When you need to rapidly dart past traffic, or make a speedy entrance up an on-ramp—even if there’s plenty of juice in the battery—the gas engine will come on and stay on for about a minute.

Right for the Wrong Reasons

Some observers—and Toyota executives—might say that’s no big deal, because it’s the overall efficiency that matters most, and 99.9+ MPG is damn good. That argument undermines just how annoying any use of the gas engine is after you’ve become accustomed to not using it and how frustrating it is to use any gasoline when you know that you’ll be back home and charging up again with plenty of energy still in your battery pack. Moreover, I firmly believe that an EV button will become the gold standard for plug-in hybrids, and Toyota's flagship plug-in model will not have it. The lack of an EV button on the plug-in Prius would be a deal-killer for me.

2010 Prius with EV Button

The current versions of the conventional no-plug Toyota Prius feature an EV button/mode, but it only offers a few blocks of electric driving. It makes no sense to remove the EV button on the plug-in version of the Prius, which could put it to better use.

Don’t get me wrong: I loved driving the Prius Plug-in Hybrid. To me, it’s more spacious and functional than the current EV and PHEV offerings—and the proven aerodynamic platform of the Prius is a winner. Also, after the bigger battery is depleted, the plug-in Prius reverts to a 50-mpg hybrid, whereas the Volt and F3DM can only muster (charge-sustain) mileage in the mid-30s.

To more than double my 2006 Prius’s efficiency to 99.9+ MPG would be delightful—which brings to my other gripe: Toyota should graciously offer one more decimal point on the MPG reading so drivers can see just how far over 100 miles-per-gallon they can go.

Learning from Past Mistakes

In the first two generations of the conventional Prius, Toyota gave an EV button to the Japanese and European versions of the car—but removed it from U.S. drivers. It was the discovery of that EV button that led American advocates to start hacking the Prius by adding an aftermarket EV button into the vacant dashboard slot, and putting in more battery storage and a plug. The ability for advocates, like CalCars, to turn the regular Prius into a plug-in hybrid helped wake up the entire auto industry into the vast opportunity of producing factory-built plug-in hybrids and electric cars.

Toyota eventually woke up to the appeal and usefulness of the EV button, and now offers it as a standard feature in the third-generation Prius. I reached out to my contacts at Toyota and encouraged to not make the same mistake with the 2012 Prius Plug-in Hybrid that they did with the early Prii.

Their response: “Let's just say we're very aware of the issue of no EV button. It hasn't escaped us at all.” That sounds promising.

UPDATE 3/1/11: Toyota informed that the Prius Plug-in Hybrid will have an EV button. The primary purpose of the EV button will be to allow drivers to turn OFF the electric mode, and drive in conventional hybrid, in order to save those electric miles for later use.

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