Page | 1
Common faults and optimizing of Toyota Prius HEVs
W.N.L. Weerakkody
100573H
EE 3202
Department of Electrical Engineering
EE 3203
Page | 2
Contents
Page No
1. Abstract 3
2. Introduction 4
3. Literature Review 6
4. Objective 9
5. Work 10
6. Common Parts & Terminology 10
7. What is Synergy Drive? 12
8. Faults & Problems in HEVs 13
9. Manufacturer faults in Prius HEVs 14
10. Optimizing fuel 16
11. Acknowledgement 18
12. Reference 19
13. Appendices 20
Page | 3
Abstract
Hybrid Electric Vehicles or HEVs are becoming visible to us on roads increasing the number day-by-
day due to its growing popularity in an exponential manner. According to sources, today, we have
about 6 million hybrid electric vehicles worldwide and the truth is almost 4 million out of that 6
million has been sold during the last couple of years and by that, we can measure the trend to buy
HEVs. I chose this subject “Common faults and optimizing of HEVs” since we see a huge trend in
HEVs in Sri Lanka as well.
First, I personally contacted quite a few hybrid users and asked them about the problems they faced
and about the pros and cons of the HEVs they use and a selected set of observations are attached at
the appendix. Then I visited Toyota Lanka and Arabian Motors Ltd where Hybrid repairing and
services has been done throughout the time even when HEVs were not that famous in Sri Lanka.
Most common faults that I came across were,
Inverter water pump fault
Horn wiring fault
Front wheel bearing fault
Countermeasure part fault
Electric power steering (EPS) pinion shaft nut fault
Power window switch fault
Braking system fault
HID light system fault
The problem is that almost for all these faults you have to replace the part.
Then I tried to find out that how can we optimize a drive cycle of a Prius. For that one, the
conclusion that I received was sooth acceleration, smooth braking and keeping the battery at a
charge around 60%.
Page | 4
Introduction
What is a HEV? First and foremost, HEV stands for “Hybrid Electric Vehicle”.
As the Wikipedia claims “HEV” or a “hybrid electric vehicle” is a type of hybrid vehicle which
combines a conventional internal combustion engine (ICE) propulsion system with an electric
propulsion system.
The popularity of these hybrid electric vehicles started to rise up exponentially in the recent past and
hence many people were interested in buying HEVs. Many myths and stories related with it grew
among the general public as well. It is high time to solve these mysteries because day-by-day, the
gasoline oil prices are climbing sky high and we are running short of petrol as predicted by the
analysis of oil repositories and it is said that the remaining oil would be enough only for 30 more
years. So, to save fuel, it is better to switch into HEVs instead of conventional vehicles since it has
become the most reliable technology that is adopted into vehicles up to now. There are technologies
like the “air car” concept, “fuel cell” vehicles and hydrogen vehicles. But yet, the most successful
solution is the hybrid electric vehicle.
The presence of the electric powertrain (which will be described later in a chapter) is intended to
achieve either better fuel economy than a conventional vehicle or better performance. Many types
of hybrid electric vehicles are available today. We categorize them by degree to which they function
as an electric vehicle and so on.
Modern HEVs make use of efficiency-improving technologies such as regenerative braking, which
converts the vehicle's kinetic energy into electric energy to charge the battery, rather than wasting it
as heat energy as conventional brakes do which will be described in a chapter below. Some varieties
of HEVs use their internal combustion engine or ICE to generate electricity by spinning an electrical
generator (this combination is known as a motor-generator), to either recharge their batteries or to
directly power the electric drive motors which happens differently in different kinds of hybrids like
series hybrids and parallel hybrids. Many HEVs reduce idle emissions by shutting down the internal
combustion engine at idle and restarting it when needed in the hybrid electric vehicles. This
phenomenon is known as a start-stop system. Hybrid electric vehicles produce less emission from its
ICE than a conventional gasoline car of same caliber, since an HEV's gasoline engine is usually smaller
than a comparably-sized pure gasoline vehicle because it optimizes gasoline with the use of electric
power as well as optimizing the fuel supplied. If not we use the energy taken from burnt fuel to
directly drive the car, it can be geared to run at maximum efficiency, further improving fuel
economy.
As I mentioned before, here in Sri Lanka people have many myths about HEVs. One such thing is
manufacturer faults. The most significant of them is that people believe that the batteries of HEVs
are not good and not durable enough. But it is not true. Yes. The battery pack is somewhat high-
priced, but yet it is way better in performance than a usual rechargeable battery that people know
most of the times. Things like this have been addressed in this survey.
People hesitate sometimes to buy a hybrid over conventional cars as they are not satisfied enough
with the fuel economy of the car and some say that, the extra money that you have to pay for an
Page | 5
HEV is not worth at a repair after a period of time. But, by optimizing the driving style, we can
achieve higher mileage per unit fuel and that matter will also be addressed.
For this project, I selected Toyota Prius specifically since it has become the number one selling
Hybrid vehicle brand all over the world owning to more than half the number of vehicles sold all over
the world and this will be there under literature review.
There are so many myths related with HEVs. But yes, there are some very few common faults. With
this, I hope to explain the real common faults about the HEVs.
Page | 6
Literature Review
In the year 1901, Ferdinand Porsche became the first person to develop the first gasoline-electric
hybrid vehicle of the world, the Lohner-Porsche Mixte Hybrid. At that time, the hybrid electric
vehicle did not become available. The first major issue to the market was done by Toyota as a very
much upgraded version of its predecessor, the above mentioned Porche vehicle and it was the new
Toyota Prius built in Japan in 1997. Soon, it another competitor came into the market produced by
Honda and that was Honda Insight which started its production in 1999. But as early as that, the
gasoline prices in the world was very low comparing with the extra cost that you have to pay for a
hybrid electric vehicle. As far as I can remember, the diesel price in 1999, when my family bought
our first van was just Rs. 13.50 and the price of petrol was just around Rs. 50.00 according to my
memory.
Source: sundaytimes.lk
The above diagram shows the increment in fuel prices in Sri Lanka just for 2007. Around this period
of time, the fuel prices were so high and we climbing up continuously. So, due to that, hybrid electric
vehicles came to the arena since it seemed that HEVs were pretty much feasible solution for end
users since the oil price climbed and now, the price of a hybrid electric vehicle became reasonable
for people. But the things were different in other countries of the world and they became interested
in HEVs after the late 2000s and now in countries like United States of America, they have ten-
thousands of hybrid electric vehicles available for sale and they have become pretty much affordable
as well as reliable for people.
It is said that, around 6 million hybrid electric vehicles have been sold worldwide up to now. Just
note that the world population is around 6 billion and there are 6 million hybrid electric vehicles in
the world. The most number of HEVs have been produced by Toyota Motor Company selling around
4.5 – 5 million Toyota hybrid and Lexus hybrids (Lexus belongs to Toyota as well) up to now. They are
distantly followed by Honda Motor Co., Ltd. by selling around 1 million hybrids up to now and Ford
Motor Corporation selling around 0.2 million hybrids mostly in USA up to now. Toyota and most of
the other HEV selling companies have an incredible growth in selling hybrids with Toyota selling 4
million hybrids within just below 3 years. That is 2/3 of their all-time hybrid electric vehicle sales
Page | 7
Toyota Prius being the leader not only in Sri Lanka, but also in the world arena selling around 3
million units around the globe.
Hybrid electric vehicles can be according to many factors.
First, hybrid electric vehicles can be categorized by the degree of hybridization. Those are,
Full Hybrid
Mild Hybrid
Full Hybrids
This type of hybrids is also called “strong hybrids” as well. These types can be run under 3 cases.
They can run on just the engine, or it can run on just the batteries, or it might be a combination of
both systems. These cars can be driven on battery power alone. A huge and high capacity battery
pack is needed this operation.
Examples for full hybrid systems:
Toyota's Hybrid Synergy Drive which is used in Toyota Prius and Toyota Aqua
Ford's hybrid system which is used in Ford Fusion Hybrid and Ford Escape Hybrid
Chrysler's Two-Mode Hybrid technology
Mild Hybrids
Hence the electric motor doesn’t have enough power to move the vehicle on its own, Mild hybrids
use the Internal Combustion Engine and the Electric Motor together. Mild hybrids have lesser fuel
economy than full hybrids generally and they lack some technological aspects of full hybrid
technology. Usually, they can save fuel, 15% in urban driving and 8 – 10% in overall cycle comparing
with an ordinary vehicle of same caliber. But it is yet, way less than the saving of a full hybrid. A mild
hybrid is essentially a conventional vehicle with oversize starter motor, allowing the engine to be
turned off whenever the car is coasting, braking, or stopped, yet restart quickly and cleanly. The
motor is often mounted between the engine and transmission, taking the place of the torque
converter, and is used to supply additional propulsion energy when accelerating. Accessories can
continue to run on electrical power while the gasoline engine is off, and as in other hybrid designs,
the motor is used for regenerative braking to recapture energy and Regenerative breaking will be
described a little later. As compared to full hybrids, mild hybrids have smaller batteries and a
smaller, weaker motor/generator, which allows manufacturers to reduce cost and weight.
Honda's early hybrids including the first generation Insight used this design. Starting with the 2006
Civic Hybrid, the IMA system or Integrated Motor Assist (a technology by Honda)now can propel the
vehicle solely on electric power during medium speed cruising. Another example is the 2005-2007
Chevrolet Silverado Hybrid, a full-sized pickup truck. Chevrolet was able to get a 10% improvement
on the Silverado's fuel efficiency by shutting down and restarting the engine on demand and using
regenerative braking.
Page | 8
Hybrid electric vehicles can be classified by the way in which power is supplied to the drivetrain of
the vehicle.
Parallel Hybrids
Series Hybrids
Power-Split Hybrids
Of these all, Toyota Prius Hybrid is special since it has the best fuel efficiency of its class and because
it is the best-selling HEV in the world.
Parallel Hybrids
In parallel hybrids, the Internal Combustion Engine and the electric motor are both connected to the
mechanical transmission and can simultaneously transmit power to drive the wheels, usually
through a conventional transmission. Honda's Integrated Motor Assist (IMA) system as found in the
Insight, Civic, Accord, as well as the GM Belted Alternator/Starter (BAS Hybrid) system found in the
Chevrolet Malibu hybrids are examples of production parallel hybrids. Current, commercialized
parallel hybrids use a single, small (<20 kW) electric motor and small battery pack as the electric
motor is not designed to be the sole source of motive power from launch. Parallel hybrids are also
capable of regenerative braking and the internal combustion engine can also act as a generator for
supplemental recharging. Parallel hybrids are more efficient than comparable non-hybrid vehicles
especially during urban stop-and-go conditions and at times during highway operation where the
electric motor is permitted to contribute by the embedded computer.
Series Hybrids
In series hybrids, only the electric motor drives the drivetrain, and the ICE works as a generator to
power the electric motor or to recharge the batteries. The battery pack can be recharged through
regenerative braking or by the ICE (internal Combustion Engine). Series hybrids usually have a
smaller combustion engine but a larger battery pack as compared to parallel hybrids, which makes
them more expensive than parallels. This configuration makes series hybrids more efficient in city
driving.
Power-Split Hybrids
Power-split hybrids have the benefits of a combination of series and parallel characteristics. As a
result, they are more efficient overall, because series hybrids tend to be more efficient at lower
speeds and parallel tend to be more efficient at high speeds; however, the cost of power-split the
hybrid is higher than a pure parallel. Examples of power-split (referred to by some as "series-
parallel") hybrid powertrains include current models of Lexus and Toyota.
Of all these a power-split hybrid, a full hybrid, Toyota Prius is special and let’s see what are the
common faults occur in these Prius Hybrid cars.
Page | 9
Objective
In Sri Lanka at present, there is a huge trend in Hybrid Electric Vehicles. In order to support
everybody to understand and find the common faults, drawbacks, cons and pros of HEVs, this
project is done.
Page | 10
Discussion
As hybrid cars become more and more popular exponentially, it is important to understand how
they work. Just as the name implies, a hybrid electric vehicle is a combination or hybrid of a gas and
an electric motor. The two motors work together with a number of some other factors. These added
advantages the vehicle’s fuel efficiency and lower its emissions, and overcome the shortcomings
that each type of engine has on its own. Hybrids use advanced technology to wring every mile out of
each gallon of gas or watt of electric power. Hybrid vehicles have been around for a long time, many
locomotives are diesel-electric hybrids and some cities have diesel-electric buses. However, it is only
in recent years that gas-electric hybrid passenger vehicles have become popular.
Common Parts and Terminology
All gas-electric hybrids have certain parts in common. The following list describes these most
common parts of them.
Gas Engine
This is a gas engine like most cars have except that it is smaller. Most hybrids have 3-cylinder engines
that produce 65 to 80 horsepower. These engines are usually outfitted with advanced technologies
that help them run more efficiently. Hybrid cars have a fuel tank like any normal vehicle.
Electric Motor
The electric motors are very sophisticated and expend energy to get the vehicle moving but also
generate and store electricity through technologies such as regenerative braking and in idling.
Generator
The generator's sole job is to produce electrical power.
Battery
It stores the electrical energy that the vehicle produces and is needed to power the electric engine.
Transmission
A transmission on a hybrid vehicle does the same thing the transmission does on a normal car, it
transfers power to the wheels. There are two main types of transmissions in gas-electric hybrid
vehicles, parallel or series.
Parallel Transmission
Parallel transmission allows both the gas and electric engine to turn the transmission. Computer
controls help these components work together in the most efficient way possible. The electric motor
will do a lot of the work at low speeds and let the gas engine take over as speed climbs.
Page | 11
Series Transmission
In series transmission, the electric motor is the only motor that is connected to the transmission. The
gas engine is connected to a generator and is used to generate electrical energy. An onboard
computer determines what percentage of power comes from the battery pack and how much comes
from the generator.
In addition to these parts, hybrids use other tricks and technologies to improve fuel efficiency and
lower emissions.
Regenerative Braking
Brakes remove energy from a moving car. A hybrid car captures some of this energy and stores it in
the battery pack. The electric motor slows the car and by acting as a generator it charges the
batteries.
Regenerative braking and regenerative brakes are features that can be found in fully electric and
gas-electric hybrid vehicles. Cars like the hybrid Toyota Prius, Ford Fusion Hybrid and Honda Insight,
and the fully electric Tesla Roadster feature regenerative braking systems.Regenerative braking
systems capitalize on the similarities in construction of electric motors and electric power
generators. An electric motor's interior is made up of copper windings. It uses an electromagnetic
energy field to produce torque through its main shaft when power is applied to it. A generator or
dynamo is also comprised of copper windings and makes use of an electromagnetic field; applying a
force to turn its rotor allows it to produce electric power. Regenerative braking is based on the
principle of physics that states that energy cannot be destroyed; it can only be transformed from
one form to another.
Traditional Braking Systems
In a traditional braking system, pressing on the brake pedal causes a pair of brake pads in each
wheel to come into contact with the surface of a brake rotor. This contact produces friction, slowing
down and eventually stopping the vehicle. The friction itself produces heat as an energy byproduct.
Automotive engineers and designers generally perceive heat as a loss. This is the reason why,
especially in high performance cars, brake cooling systems such as air dams are employed to
dissipate heat from the brakes so that they can quickly regain their efficiency.
Regenerative Braking Systems
In a regenerative braking system, the objective is to recapture the energy byproduct that results
when the brakes are applied. In electric or hybrid automobiles, the electric motor that drives the
car's wheels plays a major part during braking. When the brake pedal is pressed, the regenerative
braking circuit switches the motor so that it now operates in reverse to counter the direction of the
wheels. This reversal actually makes it perform like a power generator or dynamo that produces
electrical energy. The electricity developed is routed towards the car's storage batteries to recharge
them. The efficiency of regenerative braking systems in use today has improved significantly. Some
existing systems are able to capture and store as much as 70 percent of the energy that would
otherwise have been lost. At higher speeds, regenerative brakes still require the assistance of
traditional brake systems to be applied as a backup. This recapturing and storing of electrical energy
Page | 12
may be likened to "trickle" charging of the batteries. This is because most of the time, the electric
motor runs in torque producing mode to drive the vehicle. The recommended battery charging
method still has to be performed to charge the batteries fully, although regenerative braking does
translate to an increase in vehicle range.
Idle Off
A hybrid will turn the gas engine off when the car is stopped at a light or stop sign. The electric
engine then powers the car as you start up again and switches to the gas engine or generator as
higher speeds are reached.
Advanced Materials and Design
Hybrids use lightweight materials like aluminum and carbon fiber to reduce the weight of vehicle.
Aerodynamic designs help cut back on drag helping to increase fuel efficiency.
All of these technologies combined help produce some very impressive gas mileage statistics. As
these technologies improve we will see greater increases in fuel efficiency, and advances like plug in
hybrids may eventually eliminate the need for gasoline altogether for short commutes.
How does a HEV work
What is Synergy Drive?
Toyota Prius has a very fuel efficient complex hybrid synergy drive system. These systems, pioneered
by the Toyota Prius, use a combination of gasoline and electric engines with a continuously variable
transmission to give maximum fuel economy and power delivery over a wide range of speeds and
conditions. Hybrid Synergy Drive is a drive-by-wire system with no mechanical connection between
the engine controls and the engine itself, and as such uses solely electrical signals to determine drive
train output.
Source: http://www.global-greenhouse-warming.com/images/ToyotaHybrid1.jpg
Page | 13
Overview of Operation
In a conventional internal combustion engine, a battery is used to power accessories while the
engine is turned off as well as in combination with a starter motor, which is used for starting
purposes only. An alternator powers accessories and recharges the battery while the engine is in
use, and the engine itself is the focus of the vehicle's motivation. In a Hybrid Synergy Drive or HSD
power train, the transmission, alternator and starter motor are replaced with a pair of powerful
electric motors which generate approximately 60hp, and can work either by themselves or in unison
with a conventional internal combustion engine as needed. Power distribution is controlled through
a combination of mechanical power splitter, and computer controlled shunts while the motors
themselves are powered by a battery pack and used for start-up, low speed driving and acceleration.
Internal Combustion or Electric Power on Demand
While the internal combustion engine itself may not even be active during start up, it may be used
on demand for higher road speeds, increased acceleration, or to aid in increased battery charging.
When the aid of the internal combustion engine is required, one of the electric motors may be used
as a starter. When the aid of the gasoline engine is no longer required, the engine itself may be
turned off as needed, with load shifted in full to the electric motors. This allows a hybrid engine
configuration to achieve superior fuel economy without any holes of lags in power delivery.
Regenerative Braking
It has been described above.
Hybrid Synergy Drive equipped vehicles have managed to directly address many of the downsides
found in both gasoline powered and electrically power drive trains alike, by combining their
strengths into one versatile package. It is through this unique versatility in operation that hybrid
technologies have become so successful compared to their fully electrically powered counterparts.
Also, it's one of the main reasons why this technology may become a staple in the future of
automotive technology. Now that we have knowledge in what happens in a hybrid electric vehicle,
let’s see the common faults in Priuses.
What are the main problems in Toyota Prius?
Faults and Problems in Hybrid Electric Vehicles
Electric and hybrid cars have been under some hard scrutiny since their introduction to the market
several years ago. Some of the claims critics have made against hybrids and electrics deal with parts
and maintenance. It is true that these cars require some special care, but for the most part,
naysayers have met their match with reliable vehicles that can go many years without needing any
serious maintenance.
Usual Maintenance
Page | 14
Except for the electrical counterparts, hybrid electric vehicles have the components of a regular
internal combustion engine and hence they require the same routine maintenance as any other
gasoline vehicle. This includes the usual “service” as called by Sri Lankan people and that is changing
of air filters and oil. The hybrid electric cars usually can run approximately 65,000 kilometers without
changing the air filter. There’s no need of changing oil in a hybrid electric vehicle at the same
intervals comparing with the gasoline engine-only cars because the electric motor or the battery of
the car takes some of the load off of the engine. Therefore, the car can go between 8,000 and
16,000 kilometers between oil changes. Brake pads of a hybrid car are also need to be changed less
frequently than in a conventional vehicle because of the regenerative braking properties. All other
engine maintenance is much like that for any other conventional gasoline powered car.
Battery Life
One of the biggest attacks made on hybrids has to do with battery life. It is said that the battery life
is very short, and if something were to happen to it, it is very expensive to replace. One of the keys
to keeping a battery in good repair is to keep the battery charged between 40 to 60 percent. This
way, the battery is never completely drained or charged, increasing its life. This can be maintained
strictly through regenerative braking.
Manufacturer faults of Toyota Prius HEVs
There are two types of Toyota Prius HEVs in Sri Lanka which are very commonly used.
Toyota Prius NHW20 (2nd Generation Prius)
Toyota Prius ZVW30 (3nd Generation Prius)
Apart from these two, there are very few 1st generation vehicles as well. But since the number of
vehicles is so very low, let’s not discuss about those in detail. But as I was informed by the Toyota
Lanka, the first battery replacement they received happened recently and it was delivered to a first
generation Prius. Now, 1st generation Priuses have batteries that are old about 10-12 years and no
wonder they will have to be replaced with new batteries. I have considered many cases found in the
Internet and they have replaced their batteries after running about 200,000 kilometers. Here in Sri
Lanka, the agents, Toyota Lanka does not import batteries for HEVs. But I was informed by them that
the battery price outside is around Rs. 500,000.00 nowadays and it is a 28 cell battery. Each and
every cell can be replaces in case of such replacement and one cell would cost around Rs. 30,000.00
at present. There’s another problem in Priuses and even though here in Sri Lanka we didn’t have
much vehicles at that time, in United States of America, it recalled Prius vehicles in 2005. That was in
Highway driving, the gasoline engine shuts off. As I have described before, at speedy driving, in
Toyota Synergy Drive method, gasoline engine works at high speeds. Here, sometimes it failed in 1st
generation hybrids. These vehicles have been programmed to shut down either its gasoline engine
or the battery power supply as needed. The program had the fault and Toyota repaired it calling the
vehicles and it was not a major issue. There are some complaints from hybrid car owners concerning
the engine light coming on or staying on without necessarily indicating a particular problem with the
vehicle. This is issue seems to be common of most cars and newer ones in particular and could be a
simple sensor glitch. But since this 1st generation scenario is out of the scope of the objectives of this
project, let’s look into the main manufacturer faults in common Toyota Prius HEVs in Sri Lanka.
Page | 15
First, the production of the second generation Prius Hybrid or the Toyota Prius NHW20 was started
in 2004 by Toyota and was produced till 2009. Approximately 670,000 Prius vehicles are being
recalled in the United States to inspect and in some cases replace the steering intermediate
extension shaft recently in November 2012 on vehicles between 2004 and 2009. But yet according to
Toyota Lanka, no complaints from Sri Lanka have been received. There is a very common
manufacturer fault in these vehicles and that is the only major issue with Toyota Prius. The NHW20
has a huge problem with its Inverter Motor Pump.
“On 2004 through certain 2007 model year Prius vehicles, there is a possibility that air may remain at
the bearing of the Hybrid Electric Water Pump (HV Water Pump), causing pump actuation to be
slow. In this condition, the temperature of the coolant could rise and become high, which will result
in illumination of the Malfunction Indicator Light (check engine light "ON") for diagnostic code
P0A93 with information code 346 (Inverter cooling system malfunction).” Says Toyota website. This
condition is caused by air being introduced into the hybrid cooling system. When air is introduced
into the hybrid cooling system, it may become trapped, causing the pump actuation to be slow. In
this condition, the temperature of the coolant could rise and become high, which will result in
illumination of the Malfunction Indicator Light. Many people come to Toyota Lanka because they see
this indicator. If the amount of coolant for the inverter is insufficient or the air bleeding is
inadequate during replacement of the coolant, air can be introduced into the system. The Hybrid
Electric Water Pump (HV Water Pump) is an electrically driven coolant pump that circulates coolant
through the hybrid components to provide cooling. The HV Water Pump serves a different purpose
than the engine water pump. This situation can be seen in Sri Lanka. But in USA and Japan, there was
a major recall of Toyota Priuses to solve this issue.
Then another small issue is there commonly in the Prius NHW20. That is with its horn wiring. It is
again a common manufacturing fault. Since it is a complex electrical system in these cars, what they
do at Toyota Lanka is that they replace these units.
Then the other very common type used in Sri Lanka is the generation 3 Prius or Toyota Prius ZVW30.
According to Toyota Lanka, Japanese vehicles do not have any fault in this type. But in UK models of
Prius, There is a problem with the front wheel bearing. There has been a number of complains about
that and what they do is replacing the front wheel bearing.
Then again there’s an issue with this ZVW30 model as I was told by Toyota and sometimes with
NHW20 as well according to the reviews of the Prius users. That is called “Countermeasure part”
problem. The countermeasure part should be replaced to solve that. That can be diagnosed when a
sudden AC cutoff occurs in a Prius or by checking coolant tube, which can be diagnosed.
In Sri Lanka, the most common problems are those ones. But apart from that there are some
common, but not as common as above faults available in Prius. One such is Electric power steering
(EPS) pinion shaft nut fault. It is said that this fault is there in earlier hybrids between 2001 and 2003.
The Electric Power Steering (EPS) system provides power assistance to reduce steering effort. It
generates torque using a power steering motor and a reduction mechanism which are assembled in
the steering gear box assembly. If the steering wheel is repeatedly and strongly turned to the full-
lock position, there is a possibility the nuts securing the pinion shaft in the steering gear box
assembly may become loose. If the vehicle is continuously operated in this condition, over time, the
customer will gradually notice significant increased steering effort when making a left turn.
Page | 16
In the Internet another issue that I found was a small problem with power window switch. The
company says the switch may have a “notchy” or “sticky” feel. If owners try to use a commercial
lubricant to eliminate the condition, it could cause the assembly to melt, smoke or in the worst case,
catch on fire. Model years 2007 to 2009 are affected but Toyota says is has received no injury claims
due to the problem. Problem can be found in Camry hybrid as well.
There is another problem in Prius which is related with the braking system. Technical experts explain
the problem as a "disconnect" in the vehicle's complex anti-lock brake system (ABS) that causes less
than a one-second lag. With the delay, a vehicle going 72 kmph will have traveled nearly another 90
feet before the brakes begin to take hold. Brakes in hybrids such as the Prius operate differently
from brakes in most cars. In addition to standard brakes, which use friction from pads pressed
against drums or rotors, the electric motors in hybrids help slow them. The process also generates
electricity, which is regenerative braking that I had described above, to recharge the batteries.
Regenerative breaking and usual hydraulic braking with anti-locking braking system seems not to
work properly in some cars. It is said to happen due to a software fault in the embedded computer
system of Prius.
There is a rare problem with HID headlamps of Prius as well. There we need to replace the bulbs.
Those are the common faults in Toyota Prius.
Now, let’s briefly see what we can do to eliminate them.
As I was informed, for those main three problems that Prius has in Sri Lanka, we have to replace the
equipment. For the Inverter water pump problem, a new inverter water pump which came after
2009 should be replaced. For horn wiring and front wheel bearing issues also can be corrected by
replacing the respective units. Countermeasure part can also be replaced if there is a fault. All these
3 can be done at Toyota Lanka and at other places where are the repairs of HEVs are undertaken.
They said that there are no sufficient experts in Sri Lanka to repair these equipment rather than
replacing.
For Electric power steering (EPS) pinion shaft nut fault, the part has to be changed as well.
That sticky power window button fault is not something that usually we worry in Sri Lanka. So, no
repair has been asked to do on that as I was informed.
The braking system failure is somewhat a common problem found in Sri Lanka as well. To avoid that,
the software related to that should be upgraded. These HEVs have very sophisticated embedded
computers. So updating the software is a key to keep the car in good shape.
For the HID lamp fault which is rare here, we should replace the lamp.
Now, let’s see what we can do to optimize fuel efficiency.
Optimizing Fuel Efficiency
If mentioned in brief, fuel efficiency depends vastly on driving style of the driver.
Page | 17
First, to use the vehicle fuel efficiently, we should avoid quick acceleration. As I mentioned earlier,
Prius usually uses the electric system at lower speeds and if we accelerate quickly, the car needs
more power and to give that the internal combustion engine kicks in. Hence the fuel efficiency goes
down. We should accelerate smoothly to optimize fuel.
Smooth braking is also a method to optimize fuel. Prius uses a regenerative breaking system as I
described before. There is s hydraulic breaking system as well. At hard breaking, i.e. when you want
to stop the vehicle quickly, without regenerative breaking, hydraulic braking comes out. The
switching between slow and smooth regenerative braking and hydraulic braking is done by the
processor inside. Below, I have added a graph to describe how it switches. So regenerative braking
works only when we brake slowly and smoothly. By that way, we can optimize fuel.
Apart from that, to optimize the vehicle, it is recommended by Toyota Lanka to use Octane 95 petrol
for Toyota Prius ZVW30.
Regular engine tuneups would make the car efficient as well.
We can perform an EGR cleaning (Exhaust gas recirculation) to optimize hybrids as well.
Page | 18
Acknowledgement
My sincere gratitude should go towards Dr. Udayanga Hemapala, Senior Lecturer in the Department
of Electrical Engineering, University of Moratuwa for guiding me to study about this very interesting
and inspiring topic. My special thank goes to Dr. Asanka Rodrigo, Senior Lecturer, Department of
Electrical Engineering, University of Moratuwa for issuing me relevant letters so that I could go and
meet the relevant companies to get necessary details. As a special person, I would like to thank Mr.
Mahesh Abeysinghe, Technical Engineer, a graduate of University of Moratuwa and now working at
Toyota Lanka (Private) Limited as the Technical Engineer handling all the hybrid electric vehicles for
giving me fullest support by providing necessary information. Again, my special thanks goes to Mr.
Ranjith Salpitikorala, a vehicle importer for helping me to contact with the people repairing hybrid
electric vehicles (Arabian Motors, an engineer and Toyota Lanka). I would like to thank everybody
who gave me information about their hybrid electric vehicles and I would like to convey my heartiest
gratitude to all the other people who were always supportive.
Page | 19
Reference
Sunday Times
http://en.wikipedia.org
http://www.howstuffworks.com/hybrid-car.htm
http://www.fueleconomy.gov/feg/hybridtech.shtml
http://www.mtu.edu/hybrid/
http://www.hybridcars.com/first-gen-hybrid-batteries/
Page | 20
Appendix
Name: Mr. Muthubanda Ekanayake
Occupation: Retired Police Officer
Vehicle: Honda Insight Hybrid
Manufacture Year: 2010
Mileage after buying the vehicle: 7000 km
Average fuel consumption: 22 kilometers per liter
Pros:
Heating of the engine is very low. No need to worry about overheating.
Engine switches off at idling. So when the car is stopped at traffic, it won’t consume
much energy as usual cars do.
The display that has been provided indicates the available mileage that can be run
without refilling gasoline. It is an added advantage over many common cars of its
type. (Sedan)
He says that earlier it did cost a lot to replace a battery. Around Rs. 450,000.00. Now
as the hybrid electric vehicles have become more common in Sri Lanka, the price of
the battery unit has also reduced and according to him the value now is around Rs.
125,000.00 and one cell is around Rs. 13,000.00.
He says that it is usually should be serviced around 14,000 km run and he says that it
is an added advantage.
Cons:
He claims that since these cars are little rare to find than conventional corolla and so
on, the parts are a bit expensive.
He says that the cost for a service is around Rs. 14,000.00 – Rs. 15,000.00 and that is
a small disadvantage over usual vehicles.
Page | 21
Name: Mr. Gunasekara
Occupation: Customs Officer
Vehicle: Toyota Prius Hybrid
Manufacture Year: 2009
Mileage after buying the vehicle: 40,000 km
Average fuel consumption: 20 kilometers per liter
Pros:
He has 3 vehicles for his family and he says that the vehicle is pretty much stable.
Handling is good.
No problem with sounds coming out of the vehicle.
Cons:
Acceleration is somewhat lesser than his other vehicles.
But works well in “power mode”. i.e. acceleration is not satisfactory in “economy
mode”, but satisfactory enough on “power mode”.
Ground clearance is very low and it is not enough for Sri Lankan roads.
In the 1800cc model, interior space is very good and in 1500cc model, it is a negative
point. He owns a 1800cc model, so it can be considered as a pro for his vehicle.
When you park that vehicle in day time, since it has a huge portion of its surface
covered with glass parts, the interior gets heated up lot more than a usual vehicle
does.
Page | 22
Name: Dr. Rathnayake
Occupation: Specialist Doctor
Vehicle: Honda Insight Hybrid
Manufacture Year: 2010
Mileage after buying the vehicle: 5000 km
Average fuel consumption: 21 kilometers per liter
Pros:
Heating of the engine is very low.
At idling, electric motor works on its own so that the internal combustion engine
switches off and hence saves a lot of fuel.
Cons:
When you are at a small slope uphill, acceleration is not enough comparing with
other cars. He owns 4 vehicles and from his experience, he claims that and he says
that there are no considerable negative points of a hybrid electric vehicle.
Page | 23
Name: Mr. Nimal Senadheera
Occupation: Factory Manager, Coool beverages
Vehicle: Toyota Prius Hybrid
Manufacture Year: 2008
Mileage after buying the vehicle: 30,000 km
Average fuel consumption: 20 - 25 kilometers per liter
Pros:
Fuel efficiency is the best comparing with the vehicles he has used before, none of
them are hybrid electric vehicles though.
Has a good air conditioning system with it.
Comfortable driving experience.
Least sound comes out of the car.
Very less smoke emission.
Maintenance is easy since no need to worry about usual checking with
water/coolent levels and so on.
It indicates almost everything you need to know at the display panel.
Emits very low level of heat from the engine.
Cons:
Not steady enough comparing with the Toyota Corolla Axio that he drives. But says
that his first choice among the two cars is Prius since he travels about 3000 – 3500
kms in a month and it saves a lot for his pocket comparing with the Axio.
Page | 24
Name: Dr. Saman
Occupation: Lecturer, Faculty of Livestock, Fisheries & Nutrition, Wayamba University of Sri
Lanka.
Vehicle: Toyota Prius Hybrid
Manufacture Year: 2008
Mileage after buying the vehicle: 25,000 km
Average fuel consumption: When he bought the car, it was 28 - 30 kilometers per liter and
now, the figure is around 20 kilometers per liter according to him.
Pros:
High fuel efficiency makes the life easier for him since he travels daily from his home
to the University.
No need to do the green test. Green test is the smoke emission level test that is now
a law that is a must-to-get for any vehicle to run on the road for a particular period
of time. But hybrid electric vehicles need not to go for that test and that is an added
advantage, even though not technically.
Cons:
He claims that the price of a battery is so high that many people won’t be able to
afford it when it comes to a replacing of battery.
There is an environmental concern attached with the batteries as well according to
him. In Sri Lanka, we do not have a method to recycle these batteries. But in
developed countries, they have. Here, we have to dispose the used battery and by
that we might dump heavy metals like lead or arsenic to environment and it can
harm and unbalance environment a lot.
Ground clearance is not enough mainly because of the angle that it has been built in
order to optimize fuel by its shape. The lower part of the car comes at a small angle
and hence, the ground clearance is not equal everywhere.
Top Related