check engine YAMAHA YZ250F 2016 Repair Manual

FUEL INJECTION SYSTEM
8-31
Fault code Er-4
SymptomRegistered data cannot be received from the Yamaha diagnos-
tic tool.
Fail-safe systemAble to start engine
Able to drive vehicle
Diagnostic code No.—
Diagnostic tool display—
Procedure—
Or-
derProbable cause of malfunc-
tion and checkMaintenance job Reinstatement method
1 Connection of Yamaha diag-
nostic tool coupler.
Check the locking condition
of the coupler.
Disconnect the coupler, and
check the pins (for bent or
broken terminals and locking
condition of the pins).Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
2 Connection of wire harness
ECU coupler.
Check the locking condition
of the coupler.
Disconnect the coupler, and
check the pins (for bent or
broken terminals and locking
condition of the pins).Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
3 Wire harness continuity. Open or short circuit  Re-
place the wire harness.
light green–light greenTurn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
4 Yamaha diagnostic tool mal-
functionReplace the Yamaha diag-
nostic tool.Turn “ON” the switch on the
FI diagnostic tool sub-lead.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
5 Faulty ECU Replace the ECU.

FUEL PUMP SYSTEM
8-34
EAS1SM9330TROUBLESHOOTING
The fuel pump fails to operate.
TIP
Before troubleshooting, remove the following part(s):
1. Seat
2. Side cover (left/right)
3. Air scoop (left/right)
4. Fuel tank
5. Air filter case cover
1. Check the fuel pump system wire
harness connections.NG 
Reconnect.
OK 
2. Check the engine stop switch.
Refer to “CHECKING THE
SWITCHES” on page 8-38.NG 
Replace the engine stop switch.
OK 
3. Check fuel pressure.
Refer to “CHECKING THE FUEL
PRESSURE” on page 7-3.NG 
Replace the fuel pump.
OK 
4. Check the fuel pump system wire
harness.
Refer to “CIRCUIT DIAGRAM” on
page 8-32.NG 
Repair or replace the wire harness.
OK 
Replace the ECU.

ELECTRICAL COMPONENTS
8-41
EAS1SM9334CHECKING THE IGNITION SPARK GAP
1. Check:
• Ignition spark gap
Out of specification  Perform the ignition
system troubleshooting.
Refer to “TROUBLESHOOTING” on page 8-
4.
TIP
If the ignition spark gap is within specification,
the ignition system circuit is operating normally.
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a. Remove the spark plug cap from the spark
plug.
b. Connect the ignition checker “1”.
c. Crank the engine, and measure the ignition
spark gap “a”.
d. Crank the engine, and gradually increase
the spark gap until a misfire occurs.
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EAS1SM9335CHECKING THE SPARK PLUG CAP
1. Remove:
• Spark plug cap
(from the spark plug lead)
2. Check:
• Spark plug cap resistance
Out of specification  Replace.
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a. Connect the pocket tester ( 1k) to the
spark plug cap.
b. Measure the spark plug cap resistance.
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EAS1SM9336CHECKING THE IGNITION COIL
1. Disconnect:
• Ignition coil terminal
(from the sub wire harness)
• Spark plug cap
(from the ignition coil)
2. Check:
• Primary coil resistance
Out of specification  Replace.
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a. Connect the pocket tester ( 1) to the igni-
tion coil. Minimum ignition spark gap
6.0 mm (0.24 in)
Ignition checker
90890-06754
Oppama pet-4000 spark checker
YM-34487
2. Spark plug cap
Resistance
10.00 k
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
Primary coil resistance
2.16–2.64 
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Ignition coil terminal 1 “1”
• Negative tester probe 
Ignition coil terminal 2 “2”

ELECTRICAL COMPONENTS
8-43
EAS1SM9338CHECKING THE ECU
1. Check:
• Mounted condition of ECU.
Improperly mounted  Remount.
TIP
• The lean angle sensor is built into the ECU.
• The lean angle sensor stops the engine in
case of a turnover.
• To ensure that the lean angle sensor operates
correctly, do not change the installed condi-
tion of the ECU.
EAS1SM9339CHECKING THE STATOR COIL
1. Disconnect:
• Stator coil coupler
(from the wire harness)
2. Check:
• Stator coil resistance
Out of specification  Replace.
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a. Connect the pocket tester ( 1) to the sta-
tor coil coupler.
b. Measure the stator coil resistance.
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EAS1SM9340CHECKING THE RECTIFIER/REGULATOR
1. Check:
• Rectifier/regulator output voltage
Out of specification  Replace.
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a. Set the digital tachometer to the ignition coil.
b. Connect the pocket tester (20 VDC) to the
rectifier/regulator coupler.
c. Start the engine and let it run at about 5000
r/min.
d. Measure the output voltage.
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Stator coil resistance
0.624–0.936 
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
White “1”
• Negative tester probe 
White “2”
12
No load regulated voltage
14.1–14.9 V
Digital tachometer
90890-06760
YU-39951-B
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Red “1”
• Negative tester probe 
Black “2”
21
B
WWR

ELECTRICAL COMPONENTS
8-45
2. Check:
• Throttle position sensor maximum resis-
tance
Out of specification  Replace.
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a. Connect the pocket tester ( 1k) to the
throttle position sensor.
b. Check the throttle position sensor maximum
resistance.
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3. Install:
• Throttle position sensor
TIP
When mounting the throttle position sensor, ad-
just its angle properly. Refer to “ADJUSTING
THE THROTTLE POSITION SENSOR” on
page 7-9.
EAS1SM9343CHECKING THE THROTTLE POSITION
SENSOR INPUT VOLTAGE
1. Check:
• Throttle position sensor input voltage
Out of specification  Replace the ECU.
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a. Connect the test harness S-pressure sensor
(3P) to the throttle position sensor coupler
and the wire harness.
b. Connect the pocket tester (20 VDC) to the
test harness S-pressure sensor (3P).
c. Start the engine.
d. Measure the throttle position sensor input
voltage.
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Resistance
6.30 k
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Blue “1”
• Negative tester probe 
Black/Blue “2”
21
Throttle position sensor input
voltage
4–6 V
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
Test harness S– pressure sensor
(3P)
90890-03207
YU-03207
• Positive tester probe 
Blue “1”
• Negative tester probe 
Black/Blue “2”
21

ELECTRICAL COMPONENTS
8-46
EAS1SM9344CHECKING THE INTAKE AIR PRESSURE
SENSOR
1. Check:
• Intake air pressure sensor output voltage
Out of specification  Replace.
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a. Connect the pocket tester (20 VDC) to the
intake air pressure sensor coupler (wire har-
ness side).
b. Start the engine.
c. Measure the intake air pressure sensor out-
put voltage.
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EAS1SM9345CHECKING THE INTAKE AIR TEMPERA-
TURE SENSOR
1. Remove:
• Intake air temperature sensor
(from the air filter case)
EWA
WARNING
• Handle the intake air temperature sensor
with special care.
• Never subject the intake air temperature
sensor to strong shocks. If the intake air
temperature sensor is dropped, replace it.2. Check:
• Intake air temperature sensor resistance
Out of specification  Replace.
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a. Connect the pocket tester ( 1k/100) to
the intake air temperature sensor terminal.
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EAS1SM9346CHECKING THE NEUTRAL SWITCH
1. Remove:
• Neutral switch
2. Check:
• Neutral switch
Out of specification  Replace. Intake air pressure sensor output
voltage
3.57–3.71 V at 101.3 kPa
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Pink/Black “1”
• Negative tester probe 
Black/Blue “2”12
P/B
P/B
Intake air temperature sensor re-
sistance
290–390  at 80 °C (176 °F)
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Brown/White “1”
• Negative tester probe 
Black/Blue “2”
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
12

TROUBLESHOOTING
9-1
EAS1SM9348
TROUBLESHOOTING
EAS1SM9349GENERAL INFORMATION
TIP
The following guide for troubleshooting does
not cover all the possible causes of trouble. It
should be helpful, however, as a guide to basic
troubleshooting. Refer to the relative procedure
in this manual for checks, adjustments, and re-
placement of parts.
EAS1SM9350STARTING FAILURES
Engine
1. Cylinder and cylinder head
• Loose spark plug
• Loose cylinder head or cylinder
• Damaged cylinder head gasket
• Damaged cylinder gasket
• Worn or damaged cylinder
• Incorrect valve clearance
• Improperly sealed valve
• Incorrect valve-to-valve-seat contact
• Incorrect valve timing
• Faulty valve spring
• Seized valve
2. Piston and piston ring(s)
• Improperly installed piston ring
• Damaged, worn or fatigued piston ring
• Seized piston ring
• Seized or damaged piston
3. Air filter
• Improperly installed air filter
• Clogged air filter element
4. Crankcase and crankshaft
• Improperly assembled crankcase
• Seized crankshaft
Fuel system
1. Fuel tank
• Empty fuel tank
• Clogged fuel tank breather hose
• Deteriorated or contaminated fuel
• Clogged or damaged fuel hose
2. Fuel pump
• Faulty fuel pump
3. Throttle body
• Deteriorated or contaminated fuel
• Sucked-in airElectrical system
1. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
• Fouled spark plug
• Worn or damaged electrode
• Worn or damaged insulator
2. Ignition coil
• Cracked or broken ignition coil body
• Broken or shorted primary or secondary
coils
3. Ignition system
• Faulty ECU
• Faulty crankshaft position sensor
• Broken generator rotor woodruff key
4. Switches and wiring
• Faulty ECU
• Faulty engine stop switch
• Broken or shorted wiring
• Faulty neutral switch
• Improperly grounded circuit
• Loose connections
EAS1SM9351INCORRECT ENGINE IDLING SPEED
Engine
1. Cylinder and cylinder head
• Incorrect valve clearance
• Damaged valve train components
2. Air filter
• Clogged air filter element
Fuel system
1. Throttle body
• Damaged or loose throttle body joint
• Improperly synchronized throttle bodies
• Improper throttle cable free play
• Flooded throttle body
Electrical system
1. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
• Fouled spark plug
• Worn or damaged electrode
• Worn or damaged insulator
• Faulty spark plug cap
2. Ignition coil
• Broken or shorted primary or secondary
coils
• Cracked or broken ignition coil