Prius FAQ - GreenHybrid - Hybrid Cars

Prius FAQ


Old 04-02-2006, 07:36 PM
bwilson4web's Avatar
Engineering first
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Join Date: Oct 2005
Location: Huntsville, AL
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Default Prius FAQ

Prius FAQ [V02.00]


1) Definitions and terms
2) Driving for MPG
3) Handling (for new owners)
4) Maintenance for MPG
5) Maintenance for Long Life

FAQ Body

This FAQ is meant as an introduction to the Prius, not the last word. The 'Learn' section of has more detailed articles and use search engines to find more detailed and current reports. It is specific to the Prius hybrids and these guidelines may not work well with other hybrids.

1) Definitions and terms

1997-2000 Model - NHW10 was first generation sold only in Japan but may be found in other Pacific countries. For a detailed description of the first generation, hybrid drive system:
2001-2003 Model - NHW11 second generation known as 'Prius I' in mileage database. Also called 'Prius Classic.' It has a small rear spoiler with an air-gap that reduces drag at highway speeds.

2004-current Model - NHW20 third generation known as 'Prius II' in mileage database. A hatchback with a gap-less, rear spoiler, it has advanced warm-up, improved battery, improved transaxle, limited electric-vehicle capability and lower drag. For a more detailed technical description, the following links provide excellent introductions to the Prius II (NHW20) model:
ICE - internal combustion engine. On Prius, a 1500 cc, Atkinson engine with extended intake valve opening to reduce compression ratio to 8:1 while expansion ratio remains 13:1.

MG1 - motor generator one built into the transmission provides engine starting, non-moving electricity and balances the engine torque in the electronically controlled, continously variable transmission (CVT).

MG2 - motor generator two built into the transmission provides forward traction, regenerative braking and reverse gear.

PSD - power split device is the planetary gear in the transaxle that couples the engine, MG1 and output drive train feeding the final reduction gears and MG2. An operational model that shows operation is available at:
pulse and glide - a type of high mileage driving that involves accelerating to a target speed and using instruments to gently feather the accellerator to let the car coast down to a minimum speed with the ICE off. In one controlled test, an NHW20 and team of drivers achieved 110 MPG over a 14-mile loop.

stealth mode - to drive on electric only power. The NHW20 models can be modified with an electric vehicle mode switch. In all others, this is achieved by low speeds and gentle accelerator pressure.

THS, THS-2 - Toyota hybrid system, version 1 and version 2. The following Toyota engineering paper provides a detailed description of its performance and operation:
transaxle - the combination transmission and differential in the front-wheel drive Prius. Attached to the side of the ICE, it houses MG1, the PDS gear and MG2 and has output shafts for the front wheels.

"THE PRIUS THAT SHOOK THE WORLD" - this is a 105 page, PDF book written by Hideshiitazaki and translated by Albert Yamada and Masako Ishikawa. This unpublished book is the history of Prius development.

2) Driving for MPG

Try to preserve vehicle momentum instead of regenerative braking and startup: brake early and coast to a stop light just as it turns green; modest speeds; follow but do not tailgate large profile vehicles.

In cold weather, use a warm-up route at low speeds if possible before higher speeds. The warm-up route is long enough if the engine auto-stops at the last stop sign or light. Warmer weather can use a shorter warm-up route.

When approaching destination, drive the last 1-2 miles in electric only or stealth mode to maximize trip MPG.

Try to chain trips to minimize cooling between each destination.

Minimize speeds into a headwind or try to follow large vehicles without tailgating.

Keep your weekend MPG separate from your standard weekly commute MPG by topping off Monday morning and Friday evening.

Techniques that improve commute MPG need to be tracked as single variable changes.

Use cruise control, if comfortable with it, to minimize fuel-wasting speed variations.

In summer, park where it will be shaded and in winter, in a sunny place.

When you can, back in to park while the car is warm and it cost almost no gas. On the next trip, you will be able to drive off directly into the warm-up phase without the delay of having to back-out. Note, backing out a long driveway will shutdown the ICE, it is normal. It will restart once stopped or put in "D".

There are On Board Diagnostic (OBD) scanners that provide the additional instrumentation used for more efficient driving.

Turning off the engine requires the car to come to a complete stop and going to "P" to restart. This makes your car into a road hazard unless already stopped at a light.

During warm-up, coasting in "N" cuts the idle fuel burn in half. With the engine automaticly off, coasting in "N" provides the lowest energy coasting. However, if the ICE is running, coasting in "N" blocks electric mode and burns extra fuel. Practice use of "N" before trying it traffic.

"When it starts to look like it's time for a fill-up, . . . go the whole length of [your] commute scoping out all the gas prices for a day or two before picking a station to fill up at. [You'll] usually manage to get gas at $.15 or $.20 lower than the highest rates out there." Leahbeatle.

3) Handling (for new owners)

The North American fuel tank has a flexible bladder to minimize gas fumes but this means: (1) the tank volume can vary and (2) the mpg calculated by dividing the odometer mileage by the gallons can disagree with the mpg on the multi function display by more than 5 mpg. Also, avoid overfilling the fuel tank with gas all the way up the filler tube as this has caused several $1,000 fuel tank replacements.

The mechanical brakes are quite ordinary because the regenerative braking is handled in the transmission. Because of regenerative braking, your brake shoes tend to last 3-4 times longer than ordinary brakes.

The engine oil is just like any car and easy to change yourself or at discount places. Just insist that they not overfill it. Have them take out the excess until they do it RIGHT or you'll pay in lower mileage. The optimum level is 3/4 between the fill marks.

Get a tire gage and/or fill with nitrogen. Keep the tires as hard as possible, 42/40 works for most tires but always ask. The front tires need to be 2 psi harder for proper handling and best ABS operation.

The B mode is used for additional engine braking going down long, mountain grades. You have to press the button to move it into to B and can do this while driving. When done, just move it back to D for better MPG.

If you ever feel the car is "running away," put the car in "N", at any speed, and the car will coast and you can brake to a stop. If you can, keep the car running and take a photos of the accelerator area.

If you run out of gas in an NHW20, ". . . the car upper dash lit up with warning lights galore and the gas pedal stopped working. The specific lights were the large exclamation point in a triangle followed by the (!) light and the VSC light and the image of the engine" but no "OUT OF FUEL" indicator. You can drive a short distance with the "WARNING BATTERY DISCHARGE" light at a slow speed in electric mode directly to a gas station. Monitor the battery charge level and stop before it fully discharges . . . AAA can bring you some gas and this avoids a tow. Once filled with gas, the errors will clear. From 'Mr. Bean'. (NOTE: The transaxle oil pump runs from the ICE so minimize stress.)

Sometimes running out of gas and multiple attempt to start the car or other conditions may cause an error code that keeps the Prius from starting. Once and only once, you can clear the codes by disconnecting the negative auxiliary battery terminal for ~10 minutes and possibly restore operation.

Those who live in snowy, winter climates should mount quality ice and snow tires (marked with a snowflake in a mountain) in the winter season. On very slippery road and winter conditions, the 2004-2006 model year Prius with OEM or non-winter tires, the traction control can leave the car unresponsive even with the accelerator pressed to the floor. It does this to prevent useless tire spinning and transaxle issues. More recent Prius ECUs have an improved traction control system that will 'pulse-spin' the wheels in super slippery, icy conditions.

The optional, Vehicle Stability Control (VSC) is an electronic system designed to help the driver maintain steering control with hard steering. The standard Traction Control (TRAC) cuts power to prevent wheel spin with hard accelerator. The standard Anti-Lock Brakes (ABS) prevents a wheel from locking up with hard braking. All three systems require quality tires designed for the road surface, either paved, water, snow or ice covered.

Backup is a silent, electric operation so the NHW20 model issues a "beep" in the cabin to alert the driver when backing up. But a beep inside the cabin does not alert those outside the car and can annoy the driver. This thread started by David Gillett explains how to disable the cabin, backup beep.

When running in electric vehicle mode, speeds 1-42 mph, the motors are very quiet and inattentive pedestrians and the blind may be startled as you approach. Pay special attention in parking lots and around pedestrians at slow speeds.
Congress has legislation pending to put noise makers on hybrid electric vehicles. However, the Prius Fatality Accident Rate is half that of all vehicles as reported by the NHTSA using the Fatality Accident Reporting System (FARS) data.
"Check engine" light indicates something is wrong even if it is a minor problem. If you do not have an OBD scanner, it is best to drive or have the car towed to a Toyota service center and have them read the codes. Turning the car OFF and ON three times can sometimes clear the indication and code but it is better to know what happened.

In the NHW20 Prius, a maintenance required light will come on after 5,000 miles indicating it is time to change the oil. This can be cleared, check the owner's manual.

There is an enthusiastic community dedicated to Pulse and Glide driving. However, it is not required to get better than EPA mileage.

One good technique is to avoid speeds at or transiting 42 mph, the boundary between hybrid-mode where the ICE cycles on and off by itself and gas-always mode when the ICE runs all the time. My preference is to avoid the speed range 39-45 mph and either cruise slower or faster than this speed range.

ICE efficiency appears to fall off at speeds above 65-70 mph. Try to cruse at or below 65 mph by following, not drafting, large, slower traffic.

To minimize the risk of someone reading it out of the navigation computer, set your "Home" and "Work" way-points to public landmark near but not on either the real "Home" or "Work." The real addresses should come from you, not the navigation computer (or the registration and insurance cards in the glove compartment.)

4) Maintenance for MPG

Keep tires at maximum with 2 PSI more in front than rear for better handling. Stock tires are often run at 42/40. Recheck pressure at least every month with a trusted tire gage. Reportedly nitrogen filled tires may not require monthly pressure checks.

Keep ICE oil at 3/4 between 'empty' and 'full' to minimize ICE splash energy losses. Self-changers buy 4 Q/L, put three in and use the 4th as a topper in case the oil level goes down before the next change. Synthetics are OK but we lack empirical data comparing oils.

The transaxle oil is good to ~30k miles in the NHW11, 2001-03 Prius, and ~60K miles in the NHW20, 2004-current, before the viscosity drops below 15% of the OEM levels. The NHW11 uses Type T-IV and the NHW20 uses Type-WS. Amsoil ATF tests revealed excessive copper contamination, do not use.

In dusty areas, use a shorter change interval because there is no filter. The NHW11 has a pan that should be dropped, the magnet inspected and wiped clean. The NHW20 has no pan. There is about a 25% dilution from inaccessible drain oil and contaminants.

One of the best introductions to Prius tires is complemented by the Consumer Reports tire summary. Expect to spend more time researching and shopping for tires than just driving into a local store.

Year round, an engine block heater saves ~50 grams, ~1.8 oz., each morning for the NHW11, 2001-03 Prius and some savings for the NHW20. This is the difference between 52-54 MPG and 60-62 MPG for a 10 mile summer commute. [email protected] reports the two hour electricity cost is about half of the fuel cost.

5) Maintenance for Long Life

In high humidity and corrosive areas, check the brakes for rust frequently, including the inside of the rotors, to avoid binding and uneven rotor wear problems.

Make sure after-market electrical devices cannot drain the auxiliary, 12 VDC battery from unexpected loads. Normally the cigarette lighter is 'OFF' when the ignition is in lock position.

When jumping a dead 12 VDC battery, check and double check the polarity since a reverse connection can fry most of the expen$ive control computers instantly.

A Mazda Miata battery can replace the 12 VDC battery provided an adapter terminal kit is gotten for the smaller sized terminal, Japanese connector.

Keep the filters clean or replace frequently.

Fleet reports suggest the NHW11 models may need to have steering assembly checked. There is an extended warranty associated with the NHW11 Prius for a steering problem that gets a steering wheel shake ". . . 10 Hz oscillations turning the wheel in my hands about 10 degrees. . ."

Year round, an engine block heater saves nearly 100 ml. of gas each day due to faster warm-up. The only known source is Toyota of Canada, part C0140 00885, and it is difficult to install due to location of the receiver on backside of ICE. Avoid coolant heaters because of the lack of usable ICE coolant ports. Thanks Ken and our Japanese friends.

Use Rain-X to minimize use of windshield wipers and keep rear view mirrors clear.

Clean the throttle assembly every 30-50,000 miles for butterfly soot and sticky gunk. It tends to get sticky in cold weather but can cause starting problems any time of the year.

The Prius navigation unit can at arbitrary times, sound a "music box" chime after some way-points have been entered.

If you are down to your last key or key-fob, buy a replacement from Ebay and 'teach' the new key or key-fob to your car. If you lose the last key or key-fob, an NHW11 will require replacing the $1,600 ECU. For the NHW20, tell your Toyota service department about "TSB SS003-02".

"Put the Odometer in ODO mode (as opposed to TRIP 1 or 2), turn the car off, and then hold the odo button in while powering up. The odo will then cycle through a test pattern and when the miles driven reappears, the Maintenance light is reset." - Jeffrey N. Denenberg, 08/28/2007

There appears to be an intermittent problem with the plastic covers on the front seat hinges that can "squeek" while driving. It can be fixed by having the plastic cover(s) removed and either 'heat forming' or plastic removal to keep the metal seat parts from rubbing on the cover.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
If you would like to see a change to the FAQ, please start a new thread and quote the part(s) you want changed and the modification. This gives the community a chance to discuss the proposed change and if there is a consensus, then add the consensus update to the FAQ and increment the minor version number.

Now if someday, a change is needed and I am no longer around, whoever wants to 'take over' editing of the FAQ can make version "2.0" and tag it onto the FAQ thread. This provides a clean boundary yet leaves the historical version around for reference.

Thanks, Bob Wilson.

Last edited by bwilson4web; 10-31-2009 at 01:44 PM. Reason: Adding details about Prius fatal accident rate
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Old 11-13-2010, 08:57 PM
Join Date: Sep 2005
Location: Austin TX USA
Posts: 9
Default Re: Prius FAQ

I have more than 259,000 miles on my '04 Prius. The reason that I do not have an exact figure is that often when pressing the POWER button to start, none of the instrument panel lights come on. The engine will run fine, but the odometer, nav system, and mpg calculations do not happen.

Toyota could not help me with this problem, but after much trial and error, I have a workaround that always works.

First, open the driver's door. If the red open-door symbol on the instrument panel lights up, all is fine and proceed. If not, press the brake pedal for 3 or 4 seconds. If the instrument panel is still dead, keep foot on brake and turn the headlights on for 3 or 4 seconds. If still dead, press and hold the ODO trip button. Once the lights come on in the instrument panel, press the POWER button as usual. This has worked for me for the past 20 or 30 times.

Still have the factory brakes. Getting only 57 mpg now, with a loud front end noise that sounds like maybe CV joints or front bearings. On my company car, an '09 with 38K miles, I get 63 to 65 mpg.
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Old 01-02-2011, 07:39 PM
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Join Date: Feb 2008
Posts: 269
Default Re: Prius FAQ

Originally Posted by Chris Franks View Post
I have more than 259,000 miles on my '04 Prius. The reason that I do not have an exact figure is that often when pressing the POWER button to start, none of the instrument panel lights come on. The engine will run fine, but the odometer, nav system, and mpg calculations do not happen.

Toyota could not help me with this problem, but after much trial and error, I have a workaround that always works.
Sorry to add more to an FAQ thread but perhaps you have the problem described at
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Old 06-09-2014, 12:08 AM
fleetandre's Avatar
Join Date: Jun 2014
Location: Davao City
Posts: 3
Default Re: Prius FAQ

Excellent Info. The Toyota Prius is indeed one GREAT CAR!
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