I bought the mod from Coastal Technologies that allows electric-only operation at low speeds. Since I live in a small residential area with stop signs at every block, I thought it would be useful for short trips uptown. The cost was $55 including shipping and arrived (with a bag of Jelly Bellies) in about 2 weeks.

The unit is a microprocessor that you tap into a few of the wires on the car's computer. The instructions were very clear and the whole install took about 30 minutes. It came with all the needed taps, so there was no cutting or splicing. You have to remove a couple small dash panels to access the computer, but these were snap-ins and no sweat to remove and replace. You activate it with the cruise control stalk. It deactivates automatically when: moderate to hard acceleration, speed hits 34 miles per hour, or battery gets too low.

It works as advertised, and is very satisfying to drive around electric-only. However, it's more of a novelty than a practical mileage-booster. The battery gets down to 2-3 bars within a mile (now you know why an electric car needs so many batteries). And when it has to recharge the battery, your mileage is worse than if you hadn't drained it. So overall mileage-wise, it's probably a wash. There's no free lunch.

Would I do it again? Probably not. But I'll keep it installed, for that occasional experience of pure electric motoring.

Mike

Thanks for the post. In my opinion the EV switch is a novelty for tech freaks and geeks.

they sent you jelly beans? and the good ones too! nice.

Does it improve your overall milage, if you use it for just the first few minutes?

It can improve your mileage, but it depends on the terrain and stuff. My friend can keep the engine off with EV mode from when he leaves his house to the main road, so instead of warming up when the car barely needs any power, it warms up when the engine is being used more fully. On other trips he can get to the top of a big hill, so as he coasts down the hill it's waring up, thus milage is increased over warming up stopped at lights. But overall it doesn't make a big difference, it's mostly just the 'coolness' factor of cruising around at moderate speed and accleration without the engine coming on. It still excites me, being a big fan of EVs for so long.

2001 Prius Photos       2005 Prius Photos
'97 Prius Simulation Prius inner workings

For $55, I'd consider the mod. How does it affect the warranty of the car?

Like any new Prius owner, I'm becoming more and more aware of my MPG. I get great highway mileage on my work commute (55+), but crappy on my evening errand commute. In the 20 minutes I spend getting dinner, picking up the kids, and picking up the dog, I'll lose 2MPG on the display, which I have to make up, on my next trip to DC. If I could run the first 5-10 minutes on EV, it could make a significant difference in my MPG.

It could affect your warranty, but probably only if you abuse it by using it all the time and happen to kill the battery, although even that's highly unlikely since it won't let you use it below 3 bars. The reason it shouldn't void the warranty is because it's a real feature, not a hack. Supposedly the reason it wasn't included in the North American models was due to EPA mileage testing and not being able to calculate that, but personally I think Toyota wanted to have one market that didn't have the option so that they could compare (statistically) if it made a difference on battery longevity. If anything serious ever did go wrong that was covered under warranty it's very easy to remove so that they would never know you ever had it, and your warranty would be unaffected.

2001 Prius Photos       2005 Prius Photos
'97 Prius Simulation Prius inner workings

As Schwa says, whether it can be a net gain depends on your terrain or traffic controls. In general, if you can use the EV-only mode for short periods of otherwise terrible mileage driving, then have access to some cheap recharging (downhills, 35 miles per hour frontage roads, etc.), it can work.

For me, I like to use it late at night when things are extra quiet anyway to increase the effect of silent running. No radio, nothin'. Very peaceful.

Mike