EV & ECO indicator lights

First: you don't get an extra boost (as in: more power) with PWR mode. It only changes throttle response. That's also why you would use ECO, pressing the throttle to the same depth in ECO mode will produce less acceleration than in PWR mode. But full throttle in both modes is the same.
With the "EV indicator on the Hybrid System Indicator", do you mean the ECO indicator as in the attached picture? That lights up when the HSI bar is below half of the indicator (the darker green part) and indicates you are driving more economical than when you are using the right half of the indicator.



As for your confusion: I call the buttons buttons, not indicators. In my manual they are called like "Button PWR MODE" (translated). And are you really confused by something being called "ECO Driving Indicator Light" as opposed to "ECO Indicator"?

 

If it shows EV in your HSI that means that you are in EV mode, so your engine is shut then.

 

Did they answer your question Solana?

 

First, remove "ECO Mode indicator button" from your vocabulary. The button is a button; it indicates nothing. The indicator is on the instrument display. Two totally separate (but related) objects. Like a switch and a light.

Second, you press the eco button to put the car in ECO mode. This remaps the throttle response from the normal linear response to one that is more gentle at low throttle and then ramps up more steeply as you press closer to full throttle. Power mode does the opposite. Also, ECO mode modifies the air conditioning to use less power.

The indicator light near your speedometer indicates the mode you have selected with the button. If you're in ECO mode, it says so. If you're in PWR mode, it says so. And if you're in normal mode, it says nothing.

The indicator over on the hsi, shown by @Maarten28, shows if the car is running in an economical fashion. Is the engine in its most efficient rpm range, engine vacuum in a good range, and so on? It has to do with how you use your right foot, not what buttons you push with your fingers. It's the indicator that will help you maximize fuel economy. The one by the speedometer just reminds you which throttle response map you have selected.

Hope this is clear enough.

 

The HSI indicates what mode the car is in. The car will always choose what mode it thinks it is best to be in. You can override or tell the car what mode you prefer to be in by pressing the buttons.

For example, if you prefer to use EV, it will stay in electric mode. If you exceed the speed or push on the accelerator for EV, the car will go out of EV mode. You can drive EV mode in ECO and PWR mode as well. The difference in those two modes is, that the car is more willing to leave EV mode.

Why would you want to press the ECO button? That's telling the car you prefer to be in ECO mode at all times. The car will oblige when it can. The HSI will tell you when it succeeds.

 

Why would you not want to press the ECO button? You still have all the acceleration you would have in Normal or Power; it's just easier to keep a steady throttle opening over rough roads. Floor it and the response is the same either way.

As for EV vs HV mode, the only reason I ever wanted EV in my pre-PiP days was just to move it a short distance without the engine starting. Otherwise, I let the computer do its job. In fact, I installed a button for that very purpose.) Overriding the computer almost always gives worse mileage. There is energy lost to heat in using the battery and again in recharging it, so it's best to not run it down unnecessarily.

From the PiP owner's manual. I imagine the regular hatchback is pretty similar.

 

In the Gen 4, there are the same three modes (Eco, Normal, Pwr), but the consensus is the engineers made the "feel" of Normal mode of Gen 4 equivalent to the feel of the Gen 3 in Power mode. Having both cars, I can say the Gen 4 is definitely "peppier" off the line with the same throttle input, and I understand its basically the mapping of the accelerator pedal. It boils down to personal preference, what you get used to and what you want the car to feel like. There is no right or wrong answer as to when to use the Mode buttons.

 

Check the picture on post #7 on this thread:
EV-ECO-PWR and NONE ? | PriusChat
Note that at zero accelerator position (foot off the gas), the throttle is closed in all modes. At maximum accelerator position (floored), the throttle is wide open in all modes. The differences are at partial accelerator positions.

This gives the perception of quicker throttle response in PWR mode at the expense of less fine control of the throttle opening at lower pedal pressures and more sluggish response in ECO. But in any mode, WOT demands all the power the car has.

The Gen 4 may have totally different throttle maps, but it also has more actual horse power to work with, just as Gen 3 has more than Gen 2.

More info in this thread:
Gen3 Power Mode | PriusChat

Edit to add: By all means, continue to experiment. It's fun and helps you get a feel for the car. Just don't cone to any conclusions too quickly. There are so many variables that it's easy to think that condition A led to result B not knowing that condition X was there and had more influence.

 

I don't think it will matter much. If anything, ECO should be better because it's easier to modulate the throttle more precisely. Remember, the electric part of you power train has 100% torque at zero rpm. Either way, the traction control will keep you from spinning the tires. As long as the snow isn't too deep to plow through, I hear the Prius does great. I even saw video of one guy who had to turn around and get his Jeep because the snow was so deep that it slid up over the Prius' windshield and blocked his view. Traction was not a problem. But the snow tires are a good idea.

 

I found the Prius above average for driving in snow versus other FWD vehicles I've owned. I agree with Jerry that PWR mode won't make much of a difference and ECO might be better for control.

 

PWR mode does nothing to give you more power. It only changes the throttle response: in ECO you have to depress the throttle deeper to get the same response than in PWR. This image explains it a bit: