Hybrid Car – More Fun with Less Gas

EV Button Experience

register ::  Login Password  :: Lost Password?
Posted by Brian Withun on July 11, 2007, 7:38 pm

I'm intrigued by the EV button and I'd like to install one on my '06.
Has anybody installed this button?

I'd like to cruise in and out of the subdivision using all EV since
the speeds are so low.

If I can drive in on EV, I'll be able to deplete the battery a bit
before I park.
If I can drive out on EV, I'll delay the starting of the ICE until
absolutely necessary; when the battery gets low or I get out onto
faster roads.

It is wasteful to start a cold Prius with a full battery.  There's
nowhere to store the juice.

I also don't like turning on the car just to roll up the windows and
then having the ICE start up.

I'd like to hear from anyone who has installed this button and their
experience with both the installation process and the operation of the
button itself.

Brian Herbert Withun

Posted by Elmo P. Shagnasty on July 11, 2007, 9:00 pm

Please understand what the EV button does.

It does NOT turn your car into an electric car.

The car's software has a routine that keeps the engine off a bit longer,
depending on conditions; this would allow you, for example, to move your
car around in the driveway or whatnot without the engine running.  
(Normal operation of the car is to start the engine initially to warm up
the catalytic converter, assuming that you're going to drive away.)

In the US, Toyota doesn't invoke that routine.  The EV button simply
taps into the wiring harness of the computer such that it does invoke
that routine.

Now, should the car need to run the engine--it's particularly cold, the
battery is far enough down and needs recharged, whatever--the computer
will start the engine.  The software is ALWAYS in control, and will do
what it must to keep the system in the appropriate condition.  You could
have that EV switch all set up right, and the engine would still start.

This EV mode is good for about 1/4 mile or so.  Jockeying cars in the
driveway, yeah.  Driving out of your neighborhood--no.

You can achieve your goals yourself, with a prudent foot and a decent
charge in the traction battery.  That's no problem.  But you'll never
outwit the software, EV switch or no.

Hmmmm.  Think about this.  If you drive in on EV, you deplete the
battery a bit--perhaps below the threshold that the software likes.  So
when you come back out to the car, no matter what the position of the EV
switch, the engine will run to charge the battery.

There is no free energy here.  You can't have it both ways.

You say that "I'll delay the starting of the ICE until absolutely
necessary."  No, YOU won't delay anything.  YOU don't control the ICE.  
The software is in total control.  The EV switch tells the software to
invoke a different routine as best it can, that's all.

But warming the catalyst is a VERY important factor.  It is wasteful NOT
to warm the catalyst if you're going to drive the car.  And because
there is no free energy, you're simply trading off not driving the
engine hard now for driving the engine HARDER later on to refill the
battery that you depleted five minutes ago.

Which is better--let the engine start up immediately and go gently,
using little gas and spewing little exhaust, or hit the EV switch and
force the engine to come on later when the battery is more depleted,
forcing the engine to work harder in order both to drive the wheels and
to regnerate the battery?

No need for the EV switch here.  The Prius is just like any other
car--you can turn it ON without having it come to READY and be ready to
drive.  Just hit the power switch twice in a row, without your foot on
the brake.  Voila--the Prius "ignition" is "on," and systems that
require the "ignition" to be "on" can now be run--such as the power

Hit the power button only once with your foot off the brake, and you put
the Prius into Accessory mode (ACC)--just like any other car--so you can
run the radio and maybe the 12v power outlet.

No need for an EV switch to solve that problem.  Use the tools that are
built into the car.

Posted by Marc Gerges on July 12, 2007, 2:07 pm

My Prius is a european model with the EV button.

I am doing what you describe, moving electrically out of the low speed
residential zone and only starting the ICE at the main road. Obviously
this'll only work if you have enough juice in the battery. and you don't
have a lot of distance to cover. In the end if you deplete the battery
to a certain point you'll run on the ICE.


Posted by notaguru on July 12, 2007, 5:17 pm

I bought our '04 in Oct '03 (early adopters) and figured out the
EV button almost immediately. At first I used it with glee, but
the charm quickly went away. At a Prius Club meeting I met Dave
Hermance, a Toyota Design Center engineering manager, who said
that detection of the EV capability on the car would absolutely
void my warranty. He checked for me and said that the EV switch
usage would be recorded in the system memory, and would be
overwritten only after five restarts. Since a major failure
might make five restarts impossible, I saw no reason to retain
the EV switch, and have not missed it since.

It's easy enough to do. As I recall, just ground the correct pin
(#27, I think) in the terminal block under the rightmost dash
panel, which easily pulls away.

Posted by Greg on July 25, 2007, 8:30 pm

I get 1 to 2 miles in EV mode with this one on my '04 Prius:
(wired in parallel with the headlight dip switch)


Brian Withun wrote:

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread