Just a two second tip (now that winter is officially here...)
If you have the ECO button on and the heat is on, when you come to a stop (red light, etc.), the engine will shut off.
If the ECO button is off, the engine will keep running.

 

I also confirmed that was the case last winter. Sometimes if the motor is not warmed well, even with the ECO button on you can't get the motor to shut off. So I just don't use the heater until the motor is above 130 degrees (on the ScanGuauge), then I'll use it in the manual mode with just one or two clicks on the blower speed. Since I park in a garage, the interior even when fairly cold out is bearable without the heater until the motor warms up. I think using the heater takes more energy than using the A/C in the summertime.

 

Good point, haroldo! Thanks! Many of us forget that fact...especially where it doesn't get very cold (AZ), and we just turn the temp up a little to get the chill out in the AM. I'll remind the wife to use the seat heaters instead. But I think she is dialed in on using the EO button.

 

Appreciate the tip...I tend to forget about the ECO button. Gotta get in the habit.

 

I have observed that turning on the front windshield defroster, or turning the A/C to front windshield defrost/lower vent automatically turns off the ECO switch. When you switch to regular venting, you must again turn on the ECO switch.

The engine will shut off when the A/C system is in the mixed defrost/lower vent mode. Not sure about in full defrost mode, as the days I have had it on it has been below 20 degrees F, and I don't believe the car is getting warm enough, period.

 

With our 2010 Prius I found on one occasion, likely still partially warmed-up engine, when I bumped the target temperature on heater up/down, I could get the engine to reliably start/stop. I forget if it was in eco mode, most likely was.

 

With the deep freeze weather we had here in Colorado over the past couple of weeks, regardless of whether I had the ECO button on or not, seldom would the engine shut off. Several mornings on the way to work, the car started out with the outside air temp reading 20 degrees (was parked in the garage), then dropped to "MINUS" 12 degrees within a half mile. My average mileage dropped 4.5 MPG during the freeze. I plug the car in at night so startes off warmer in the mornings, but returning from work it takes for ever to warm up and that's where I lose a significant amount of mileage. Going up to 60 degrees on Sunday for at least 3days .. will enjoy!!
BTW -- My experience with th defrosters on in the "auto mode" will always make the engine run; however, if you run the defrosters in the "manual mode" with only one notch of fan ... the engine may shut off at stop lights if warm enough (normally over 130 degrees on the Scan Gauge).

 

It was a dumb design. After you turn them off, the ECO should return to the same selection as you had before you turned on the A/C or defrost. That would have made much more sense.