Yamaha 2004 YP400 User manual

2004
YP400(S)
5RU1-AE1
SERVICE MANUAL

EAS00000
YP400(S) 2004
SERVICE MANUAL
©2003 by Yamaha Motor Co., Ltd.
First edition, December 2003
All rights reserved.
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd.
is expressly prohibited.

EAS00002
NOTICE
This manual was produced by the Yamaha Motor Company, Ltd. primarily for use by Yamaha deal-
ers and their qualified mechanics. It is not possible to include all the knowledge of a mechanic in
one manual. Therefore, anyone who uses this book to perform maintenance and repairs on Yamaha
vehicles should have a basic understanding of mechanics and the techniques to repair these types
of vehicles. Repair and maintenance work attempted by anyone without this knowledge is likely to
render the vehicle unsafe and unfit for use.
Yamaha Motor Company, Ltd. is continually striving to improve all of its models. Modifications and
significant changes in specifications or procedures will be forwarded to all authorized Yamaha deal-
ers and will appear in future editions of this manual where applicable.
NOTE:
_
Designs and specifications are subject to change without notice.
EAS00005
IMPORTANT MANUAL INFORMATION
Particularly important information is distinguished in this manual by the following.
The Safety Alert Symbol means ATTENTION! BECOME ALERT! YOUR
SAFETY IS INVOLVED!
Failure to follow WARNING instructions could result in severe injury or death to
the scooter operator, a bystander or a person checking or repairing the scooter.
A CAUTION indicates special precautions that must be taken to avoid damage
to the scooter.
A NOTE provides key information to make procedures easier or clearer.
WARNING
CAUTION:
NOTE:

EAS00007
HOW TO USE THIS MANUAL
This manual is intended as a handy, easy-to-read reference book for the mechanic. Comprehensive
explanations of all installation, removal, disassembly, assembly, repair and check procedures are
laid out with the individual steps in sequential order.
1The manual is divided into chapters. An abbreviation and symbol in the upper right corner of
each page indicate the current chapter.
Refer to “SYMBOLS”.
2Each chapter is divided into sections. The current section title is shown at the top of each page,
except in Chapter 3 (“PERIODIC CHECKS AND ADJUSTMENTS”), where the sub-section
title(s) appears.
3Sub-section titles appear in smaller print than the section title.
4To help identify parts and clarify procedure steps, there are exploded diagrams at the start of
each removal and disassembly section.
5Numbers are given in the order of the jobs in the exploded diagram. A circled number indicates a
disassembly step.
6Symbols indicate parts to be lubricated or replaced.
Refer to “SYMBOLS”.
7A job instruction chart accompanies the exploded diagram, providing the order of jobs, names of
parts, notes in jobs, etc.
8Jobs requiring more information (such as special tools and technical data) are described sequen-
tially.

EAS00008
SYMBOLS
The following symbols are not relevant to
every vehicle.
Symbols 1to 9indicate the subject of each
chapter.
1General information
2Specifications
3Periodic checks and adjustments
4Chassis
5Engine
6Cooling system
7Fuel injection system
8Electrical system
9Troubleshooting
Symbols 0to Gindicate the following.
0Serviceable with engine mounted
AFilling fluid
BLubricant
CSpecial tool
DTightening torque
EWear limit, clearance
FEngine speed
GElectrical data
Symbols Hto Min the exploded diagrams
indicate the types of lubricants and lubrication
points.
HEngine oil
IGear oil
JMolybdenum-disulfide oil
KWheel-bearing grease
LLithium-soap- based grease
MMolybdenum-disulfide grease
Symbols Nto Oin the exploded diagrams
indicate the following.
NApply locking agent (LOCTITE®)
OReplace the part
12
34
56
78
90
AB
CD
EFG
HIJ
KLM
NO
GEN
INFO
SPEC
CHK
ADJ
CHAS
ENG
COOL
FI –+
ELEC
TRBL
SHTG
T
R
.
.
EGM
BLS M
LT
New

EAS00010
TABLE OF CONTENTS
GENERAL INFORMATION GEN
INFO 1
SPECIFICATIONS SPEC 2
PERIODIC CHECKS AND
ADJUSTMENTS CHK
ADJ 3
CHASSIS CHAS 4
ENGINE ENG 5
COOLING SYSTEM COOL 6
FUEL INJECTION SYSTEM FI 7
ELECTRICAL SYSTEM ELEC 8
TROUBLESHOOTING TRBL
SHTG 9
–+

GEN
INFO 1

GEN
INFO
CHAPTER 1
GENERAL INFORMATION
SCOOTER IDENTIFICATION..........................................................................1-1
VEHICLE IDENTIFICATION NUMBER .....................................................1-1
MODEL LABEL..........................................................................................1-1
FEATURES......................................................................................................1-2
OUTLINE OF FI SYSTEM .........................................................................1-2
FI SYSTEM................................................................................................1-3
INSTRUMENT FUNCTION .......................................................................1-4
IMPORTANT INFORMATION .......................................................................1-10
PREPARATION FOR REMOVAL AND DISASSEMBLY.........................1-10
REPLACEMENT PARTS.........................................................................1-10
GASKETS, OIL SEALS AND O-RINGS ..................................................1-10
LOCK WASHERS/PLATES AND COTTER PINS ...................................1-11
BEARINGS AND OIL SEALS ..................................................................1-11
CIRCLIPS ................................................................................................1-11
CHECKING THE CONNECTIONS ................................................................1-12
SPECIAL TOOLS ..........................................................................................1-13

GEN
INFO

1 - 1
GEN
INFO
EAS00015
GENERAL INFORMATION
SCOOTER IDENTIFICATION
EAS00017
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number 1is
stamped into the frame.
1
EAS00018
MODEL LABEL
The model label 1is affixed inside the storage
box. Record the information on this label in the
space provided. This information will be
needed when ordering spare parts.
1
SCOOTER IDENTIFICATION

1 - 2
GEN
INFO
FEATURES
EAS00896
FEATURES
OUTLINE OF THE FI SYSTEM
The main function of a fuel supply system is to provide fuel to the combustion chamber at the opti-
mum air-fuel ratio in accordance with the engine operating conditions and the atmospheric tempera-
ture. In the conventional carburetor system, the air-fuel ratio of the mixture that is supplied to the
combustion chamber is created by the volume of the intake air and the fuel that is metered by the jet
used in the respective carburetor.
Despite the same volume of intake air, the fuel volume requirement varies by the engine operating
conditions, such as acceleration, deceleration, or operating under a heavy load. Carburetors that
meter the fuel through the use of jets have been provided with various auxiliary devices, so that an
optimum air-fuel ratio can be achieved to accommodate the constant changes in the operating con-
ditions of the engine.
As the requirements for the engine to deliver more performance and cleaner exhaust gases
increase, it becomes necessary to control the air-fuel ratio in a more precise and finely tuned man-
ner. To accommodate this need, this model has adopted an electronically controlled fuel injection
(FI) system, in place of the conventional carburetor system. This system can achieve an optimum
air-fuel ratio required by the engine at all times by using a microprocessor that regulates the fuel
injection volume according to the engine operating conditions detected by various sensors.
The adoption of the FI system has resulted in a highly precise fuel supply, improved engine
response, better fuel economy, and reduced exhaust emissions.
1ECU
2Fuel injection system
relay
3Engine trouble warn-
ing light
4Lean angle cut-off
switch
5Fuel hose
6Ignition coil
7Fuel injector
8Intake air pressure
sensor
9Throttle position sen-
sor
0ISC (idle speed con-
trol) valve
AIntake air temperature
sensor
BBattery
CAir filter case
DCatalytic converter
ECrankshaft position
sensor
FCoolant temperature
sensor
GSpark plug
HFuel tank
IFuel pump
3
5
6
780
A
9B
C
2
1
4
D
E
F
G
H
I

1 - 3
GEN
INFO
FEATURES
EAS00897
FI SYSTEM
The fuel pump delivers fuel to the fuel injector via the fuel filter. The pressure regulator maintains
the fuel pressure that is applied to the fuel injector at only 250 kPa (2.5 kg/cm2, 35.6 psi). Accord-
ingly, when the energizing signal from the ECU energizes the fuel injector, the fuel passage opens,
causing the fuel to be injected into the intake manifold only during the time the passage remains
open. Therefore, the longer the length of time the fuel injector is energized (injection duration), the
greater the volume of fuel that is supplied. Conversely, the shorter the length of time the fuel injector
is energized (injection duration), the lesser the volume of fuel that is supplied.
The injection duration and the injection timing are controlled by the ECU. Signals that are input from
the throttle position sensor, crankshaft position sensor, intake air pressure sensor, intake tempera-
ture sensor and coolant temperature sensor enable the ECU to determine the injection duration.
The injection timing is determined through the signals from the crankshaft position sensor. As a
result, the volume of fuel that is required by the engine can be supplied at all times in accordance
with the driving conditions.
1Fuel pump
2Fuel injector
3Ignition coil
4ECU
5Catalytic converter
6Coolant temperature
sensor
7Crankshaft position
sensor
8Intake air pressure
sensor
9Throttle body
0Intake air temperature
sensor
AAir filter case
BThrottle position sen-
sor
CISC (idle speed con-
trol) valve
ÈFuel system
ÉAir system
ÊControl system
1
2
3
C
B
5
6
7
8
9
0
A
4
È
É
Ê
Illustration is for reference only.

1 - 4
GEN
INFO
FEATURES
INSTRUMENT FUNCTIONS
Multifunction display
WARNING
Be sure to stop the vehicle before making any
setting changes to the multifunction display.
1Clock/ambient temperature display
2Coolant temperature meter
3Fuel meter
4Odometer/tripmeters
5“SELECT” button
6“RESET” button
1V-belt replacement indicator “V-BELT”
2Fuel level warning symbol “ ”
3Coolant temperature symbol “ ”
4Oil change indicator “OIL”
The multifunction display is equipped with the
following:
• a fuel meter
• a coolant temperature meter
• an odometer (which shows the total dis-
tance traveled)
• two tripmeters (which show the distance
traveled since they were last set to zero)
• a fuel reserve tripmeter (which shows the
distance traveled since the bottom segment
of the fuel meter and fuel level warning
symbol started flashing)
• a self-diagnosis device
•aclock
• an ambient temperature display
• an oil change indicator
• a V-belt replacement indicator
NOTE:
• Be sure to turn the key to “ON” before using
the “SELECT” and “RESET” buttons.
• When the key is turned to “ON”, all of the dis-
play segments of the multifunction display
will appear one after the other and then dis-
appear, in order to test the electrical circuit.
CAUTION:
If bars 1appear where the odometer and
tripmeters are normally displayed, the
multi-function display is malfunctioning.
Replace the entire multi-function display.
1
2
3
5
6
4
3412
1

1 - 5
GEN
INFO
FEATURES
Odometer and tripmeter modes
Pushing the “SELECT”button switches the
display between the odometer mode “ODO”
and the tripmeter modes “TRIP”in the follow-
ing order:
ODO →TRIP (top) →TRIP (bottom) →ODO
When approximately 2.8 L (0.62 Imp gal,
0.74 US gal) of fuel remains in the fuel tank,
the bottom segment of the fuel meter and fuel
level warning symbol will start flashing, and the
display will automatically change to the fuel
reserve tripmeter mode “TRIP F”and start
counting the distance traveled from that point.
In that case, pushing the “SELECT”button
switches the display between the various trip-
meter and odometer modes in the following
order:
TRIP F →TRIP (top) →TRIP (bottom) →
ODO →TRIP F
1Fuel reserve tripmeter
To reset a tripmeter, select it by pushing the
“SELECT”button, and then push the “RESET”
button for at least one second. If you do not
reset the fuel reserve tripmeter manually, it will
reset itself automatically and the display will
return to the prior mode after refueling and
traveling 5 km (3 mi).
1
Fuel meter
With the key in the “ON”position, the fuel
meter indicates the amount of fuel in the fuel
tank. The display segments of the fuel meter
disappear towards “E”(Empty) as the fuel level
decreases. When the fuel level reaches the
bottom segment near “E”, the fuel level warn-
ing symbol and the bottom segment will flash.
Refuel as soon as possible.
CAUTION:
If the fuel level is not displayed and the fuel
level warning symbol, triangular mark, “E”
line, and “F” line flash in the fuel meter, the
fuel level monitoring system is malfunc-
tioning. Check the fuel sender and the elec-
trical circuit.

1 - 6
GEN
INFO
FEATURES
Coolant temperature meter
With the key in the “ON”position, the coolant
temperature meter indicates the temperature
of the coolant. The coolant temperature varies
with changes in the weather and engine load.
If the top segment and coolant temperature
symbol flash, stop the vehicle and let the
engine cool.
CAUTION:
Do not operate the engine if it is over-
heated.
Oil change indicator “OIL”
This indicator flashes at the initial 1,000 km
(600 mi), then at 5,000 km (3,000 mi) and
every 5,000 km (3,000 mi) thereafter to indi-
cate that the engine oil should be changed.
After changing the engine oil, reset the oil
change indicator. Refer to “To reset the oil
change indicator”. If the engine oil is changed
before the oil change indicator comes on (i.e.
before the periodic oil change interval has
been reached), the indicator must be reset
after the oil change for the next periodic oil
change to be indicated at the correct time.
The electrical circuit of the indicator can be
checked according to the following procedure.
1. Set the engine stop switch to “”and turn
the key to “ON”.
2. Check that the indicator comes on for a few
seconds and then goes off.
3. If the indicator does not come on, check the
electrical circuit. Refer to “SIGNALING
SYSTEM”in chapter 8.
NOTE:
The oil change indicator may flash when the
engine is revved with the scooter on the cen-
terstand, but this does not indicate a malfunc-
tion.

1 - 7
GEN
INFO
FEATURES
To reset the oil change indicator
1. Turn the key to “ON”.
2. Hold the reset button pushed for two to
eight seconds.
1Reset button “OIL CHANGE”
3. Release the reset button, and the oil
change indicator will go off.
NOTE:
If the engine oil is changed before the oil
change indicator comes on (i.e. before the
periodic oil change interval has been reached),
the indicator must be reset after the oil change
for the next periodic oil change to be indicated
at the correct time. To reset the oil change
indicator before the periodic oil change interval
has been reached, follow the above proce-
dure, but note that the indicator will come on
for 1.4 seconds after releasing the reset but-
ton, otherwise repeat the procedure.
V-belt replacement indicator “V-BELT”
This indicator flashes every 20,000 km
(12,000 mi) when the V-belt needs to be
replaced.
The electrical circuit of the indicator can be
checked according to the following procedure.
1. Turn the key to “ON” and make sure that the
engine stop switch is set to “ ”.
2. If the indicator does not come on, check the
electrical circuit. Refer to “SIGNALING
SYSTEM” in chapter 8.
To reset the V-belt replacement indicator
1. Turn the key to “ON” and make sure that the
engine stop switch is set to “ON”.
2. Disconnect the V-belt replacement reset
coupler 1for two to ten seconds.
3. And then, connect the V-belt replacement
reset coupler, the V-belt replacement indica-
tor will come on for 1.4 seconds.
And the V-belt replacement indicator will go
off.
NOTE:
If the V-belt is replaced before the V-belt
replacement indicator comes on (i.e. before
the V-belt replacement interval has been
reached), the indicator must be reset after the
V-belt replacement for the next periodic V-belt
replacement to be indicated at the correct
time.
1
1

1 - 8
GEN
INFO
FEATURES
Self-diagnosis device
This model is equipped with a self-diagnosis
device for various electrical circuits.
If any of those circuits are defective, the multi-
function display will indicate a two-digit error
code (e.g., 12, 13, 14).
If the multifunction display indicates an error
code, note the code number, and then check
the vehicle. Refer to “FUEL INJECTION SYS-
TEM”in chapter 7.
CAUTION:
If the multifunction display indicates an
error code, the vehicle should be checked
as soon as possible in order to avoid
engine damage.
This model is also equipped with a self-diagno-
sis device for the immobilizer system.
If any of the immobilizer system circuits are
defective, the immobilizer system indicator
light will flash, and then the multifunction dis-
play will indicate a two-digit error code (e.g.,
51, 52, 53) when the key is turned to “ON”.
NOTE:
If the multifunction display indicates error code
52, this could be caused by transponder inter-
ference. If this error appears, try the following.
1. Use the code re-registering key to start the
engine.
NOTE:
Make sure there are no other immobilizer keys
close to the main switch, and do not keep
more than one immobilizer key on the same
key ring! Immobilizer system keys may cause
signal interference, which may prevent the
engine from starting.
2. If the engine starts, turn it off, and try start-
ing the engine with the standard keys.
3. If one or both of the standard keys do not
start the engine, re-register the standard
keys.
If the multifunction display indicates an error
code, note the code number, and then check
the vehicle. Refer to “IMMOBILIZER SYSTEM”
in chapter 8.

1 - 9
GEN
INFO
FEATURES
Clock mode
To set the clock:
1. Push the “SELECT”button and “RESET”
button together for at least two seconds.
2. When the hour digits start flashing, push
the “RESET”button to set the hours.
3. Push the “SELECT”button, and the minute
digits will start flashing.
4. Push the “RESET”button to set the min-
utes.
5. Push the “SELECT”button and then
release it to start the clock. Pushing the
“RESET”button for at least two seconds
switches the clock display to the ambient
temperature display.
Ambient temperature display
This display shows the ambient temperature
from –10 °C to 50 °C in 1 °C increments. The
temperature displayed may vary from the
ambient temperature. Pushing the “RESET”
button for at least two seconds switches the
ambient temperature display to the clock dis-
play.
•When the ambient temperature falls below
–10.0 °C, “–10.0 °C”is displayed.
•When the ambient temperature climbs
above 50.0 °C, “50.0”is displayed.
NOTE:
•If “– –°C”is displayed or “50.0”flashes while
the ambient temperature is between –10.0 °C
and 50.0 °C, there is a problem with the elec-
trical circuit. Check or repair the electric cir-
cuit or replace the thermistor.
•The accuracy of the temperature reading
may be affected when riding slowly (approxi-
mately under 20 km/h) or when stopped at
traffic signals, railroad crossings, etc.