Review of 2007 Toyota Prius

The Prius is a really some kind of futuristic flying saucer cunningly disguised to look like a car. Warp this baby back to 1980 and the natives wouldn't be able to fix it. Heck, you can't even push it if the batteries die. For instance:
- it doesn't have a regular engine, it has two 3-phase AC motor-generators powered by a liquid-cooled inverter and voltage booster.
- it has a nickel-metal-hydride battery with temperature sensors and a computer-controlled ventilation system
- it has touch-screen controls for the climate-control and audio systems, like the 767 airliner
- it has a fly-by-wire control system like a military jet, with yaw sensors and an optional gyrocompass
- it has an aerodynamic resistance coefficient of 0.26, achieved with things like underbody panels and air dams around the wheels
- it doesn't have an ignition switch, it has a power button and an electronic immobilizer key. With the optional "smart key", you don't even have to remove it from your pocket to drive
- it continues to operate under computer control even when supposedly "turned off", running pumps and ventilation systems autonomously

Why Prius ?

We were looking for something with significantly better fuel economy and lower emissions than a regular car. In the current Canadian market, that means a hybrid. There seem to be no viable battery/electric or fuel cell cars available at this time.

Many car manufacturers are still advertising how powerful their cars are, or how fast, or how well they perform on winding highways with no other cars in sight. As if most drivers ever see roads like that (OK, the Duffy Lake road is pretty neat).

The Prius, on the other hand, is great for real life - being stuck in traffic. The gasoline engine cuts out, and it will creep forward quietly on battery power with zero emissions. Or, with the EV button (standard in Europe, for North America see here or google "Prius EV mod"), you can maybe make it to the corner store on battery alone.
(don't bother; the EV switch is a gimmick - good for backing the car out to wash it, or sneaking across the mall car park from the drugstore stalls to the bank stalls. The lights still come on, so it's not quite "stealth")

How does it work ?

Pretty well, considering. (no, really). The official website is (Canada) or (USA), but it's hard to find much technical information. The best publicly available description may be in the Emergency Response Manual and Dismantling Manual. Full manuals may be bought or viewed online for a fee (a few Euros) at or (US only)

Essentially, the Prius has a gasoline engine and two electric motor-generators connected to a planetary gear system which drives the front wheels. Electric power is provided from a 200V NiMh battery via a fluid-cooled inverter. The motor-generators provide regenerative braking, 100% of the power in reverse, and extra power for acceleration. The Prius doesn't actually have any gears in the normal sense; the gasoline engine normally runs at a fuel-efficient low-emission rpm and one of the motor-generators adjusts the torque on the other end of the planetary gear to give the desired road speed. Think of a normal car with the left driving wheel spinning on ice and the right one stationary - by braking the left wheel you could transfer some torque to the right one to move forward. (Later) - I realize now that the preceding sentence is rubbish, at least the bit about always running at an efficient RPM. From the RPM-speed graph further down, it is clear the engine RPM is all over the place. It does spend a fair bit of time at about 1300 RPM, though, which is probably the battery-charging regime.

It is not possible - at least, in the factory-standard model - to charge the NiMH battery in any other way, so you are still dependant on gasoline, though Hymotion makes a conversion kit.

A small 12V lead-acid battery provides power to run the computers, lights, and control systems. It is recharged from the HV system via a DC-DC converter. As far as I can determine, it cannot be used to start the car; the motor-generator is needed for that, powered by the high-voltage battery. But if it runs flat the door locks won't work. (Since the 12V battery is in the back, which won't open without power, you have to connect jump cables to the fuse box next to the engine)


Pretty good, IMO. OK, it's not going to win drag races or tow a 2000kg boat, but it did OK on our trip across the mountains, taking the grades without gasping for breath and overtaking most everything on the road (100kph limit, and 30k over risks a ticket for dangerous driving, so it's no autobahn...). The stock tires are a bit iffy on ice, though.

Easter Egg

Holding the "Info" button down on the centre console while turning the lights on and off brings up a diagnostic display.


Road Trip

About 1720 km through the Rockies from Vancouver to Prince George and back, plotting energy consumption against elevation: PG.html


stuff I'd change if I could


Things that look interesting to follow up on: ...bought an OBDScan-APEX; so far read OBD-II data as per OBD-II_PIDs (wikipedia)

RPM vs. speed, in city. When RPM = 0 but speed > 0, engine is turned off.

August 2008. Drove from Vancouver to La Jolla (near the Mexican border) via Las Vegas, San Francisco, Death Valley, Anaheim (not necessarily in that order).
The air conditioning held 23C inside with 45C outside - pretty impressive. Ran out of gas on I5 and all sorts of warning lights came on ("take to dealer"). Battery got us to a rest area where I bought some gas from an ATV owner (thanks!) and all the warnings disappeared.
Long steep grades in the US Rockies used up the battery more than trips in the Canadian Rockies. The battery indicator was nearly on zero and I guess we had less power available than normal, but this was on really twisty roads and we couldn't have used it anyway. When stopping after a long climb, I let the engine run awhile to recharge the 500V battery (really don't want to e unable to start the engine; there is no possibility of a jump start, unless off another Prius whose owner doesn't mind voiding the warranty)

Sept. 2008. Bought a hitch kit to support a bicycle carrier. There's lots of these now; they all look much the same and bolt on to body in place of the tie-down brackets. You have to cut the plastic underbody cover somewhat.