2014 YAMAHA YZ250F oil

IGNITION SYSTEM
8-3
EAS1SM1323
1. Crankshaft position sensor
2. AC magneto
3. Rectifier/regulator
4. Joint connector
5. Condenser
7. Engine stop switch
9. ECU
10.Ignition coil
11.Spark plug

IGNITION SYSTEM
8-4
TROUBLESHOOTING
The ignition system fails to operate (no spark or intermittent spark).
TIP
Before troubleshooting, remove the following part(s):
1. Side cover (left/right)
2. Seat
3. Fuel tank
4. Air scoop (left/right)
5. Air filter case cover
1. Check the ignition system wire har-
ness connections.NG 
Reconnect.
OK 
2. Check the spark plug.
Refer to “CHECKING THE SPARK
PLUG” on page 3-35.NG 
Correct or replace the spark plug.
OK 
3. Check the ignition spark gap.
Refer to “CHECKING THE IGNI-
TION SPARK GAP” on page 8-41.OK 
The ignition system circuit is OK.
NG 
4. Check the ignition coil.
Refer to “CHECKING THE IGNI-
TION COIL” on page 8-41.NG 
Replace the ignition coil.
OK 
5. Check the engine stop switch.
Refer to “CHECKING THE
SWITCHES” on page 8-38.NG 
Replace the engine stop switch.
OK 
6. Check the crankshaft position sen-
sor.
Refer to “CHECKING THE CRANK-
SHAFT POSITION SENSOR” on
page 8-42.NG 
Replace the crankshaft position sensor.
OK 
7. Check the stator coil.
Refer to “CHECKING THE STA-
TOR COIL” on page 8-43.NG 
Replace the stator coil.
OK 

CHARGING SYSTEM
8-8
TROUBLE SHOOTING
The condenser is not being charged.
TIP
Before troubleshooting, remove the following part (s):
1. Seat
2. Air scoop (left)
1. Check the entire charging system’s
wiring.NG 
Reconnect.
OK 
2. Check the rectifier/regulator.
Refer to “CHECKING THE RECTI-
FIER/REGULATOR” on page 8-43.NG 
Replace the rectifier/regulator.
OK 
3. Check the stator coil.
Refer to “CHECKING THE STA-
TOR COIL” on page 8-43.NG 
Replace the stator coil.
OK 
4. Check the charging system wire
harness.
Refer to “CIRCUIT DIAGRAM” on
page 8-6.NG 
Repair or replace the wire harness.
OK 
Replace the condenser.

FUEL INJECTION SYSTEM
8-23
Fault code 33
SymptomIgnition coil: open or short circuit detected in the primary lead
of the ignition coil.
Fail-safe systemUnable to start engine
Unable to drive vehicle
Diagnostic code No.30
ActuationActuates the ignition coil five times at one-second intervals.
“WARNING” on the Yamaha diagnostic tool blinks five times when-
ever the ignition coil is actuated.
ProcedureCheck that a spark is generated five times.
• Connect an ignition checker.
Or-
derProbable cause of malfunc-
tion and checkMaintenance job Reinstatement method
1 Connection of ignition coil
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.After starting the engine, idle
this and wait about 5 sec-
onds.
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.After starting the engine, idle
this and wait about 5 sec-
onds.
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.
Between ignition coil coupler
and ECU coupler.
orange–orangeAfter starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
4 Mounted condition of ignition
coil.
Check for looseness or
pinching.
Check the mounted condition
for correctness.Improperly mounted ignition
coil  Remount or replace
the ignition coil.After starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
5 Defective ignition coil (test
the primary coils for continu-
ity).Check the primary resistance
of the ignition coil.
“CHECKING THE IGNITION
COIL” on page 8-41.After starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.

FUEL INJECTION SYSTEM
8-24
TIP
Disconnect the fuel pump coupler when this diagnostic tool is used. 6 Faulty ECU Execute the diagnostic mode.
(Code No. 30)
No spark  Replace the
ECU.
Fault code 39
Symptom Injector: open or short circuit detected.
Fail-safe systemUnable to start engine
Unable to drive vehicle
Diagnostic code No.36
ActuationActuates injector five times at one-second intervals.
“WARNING” on the Yamaha diagnostic tool blinks five times when
the injector is actuated.
ProcedureCheck that injector is actuated five times by listening for the oper-
ating sound.
Or-
derProbable cause of malfunc-
tion and checkMaintenance job Reinstatement method
1 Connection of injector cou-
pler.
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.After starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
2 Defective injector. Check the injector.
“CHECKING THE FUEL IN-
JECTOR” on page 8-47.After starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order.
3 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.After starting the engine, idle
this and wait about 5 sec-
onds.
Fault code No. is not dis-
played  Repair is finished.
Fault code No. is displayed 
Go to next order. Fault code 33
SymptomIgnition coil: open or short circuit detected in the primary lead
of the ignition coil.

ELECTRICAL COMPONENTS
8-37
EAS1SM1335
1. Rectifier/regulator
2. Intake air pressure sensor
3. Throttle position sensor
4. Injector
5. Intake air temperature sensor
6. ECU
7. Ignition coil
8. Condenser
9. Neutral switch
10.Coolant temperature sensor

ELECTRICAL COMPONENTS
8-41
EAS1SM1336CHECKING 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.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1337CHECKING 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.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1338CHECKING 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.
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
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
Spark plug cap resistance
10 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
8-42
b. Measure the primary coil resistance.
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3. Check:
• Secondary coil resistance
Out of specification  Replace.
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a. Connect the pocket tester ( 1k) to the ig-
nition coil.
b. Measure the secondary coil resistance.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1339
CHECKING THE CRANKSHAFT POSITION
SENSOR
1. Disconnect:
• Crankshaft position sensor coupler
(from the wire harness)
2. Check:
• Crankshaft position sensor resistance
Out of specification  Replace.
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Connect the pocket tester ( 100) to the
crankshaft position sensor coupler.
b. Measure the crankshaft position sensor re-
sistance.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1340
Secondary coil resistance
8.64–12.96 k
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Ignition coil terminal 1 “1”
• Negative tester probe 
Spark plug lead “2”
Crankshaft position sensor resis-
tance
228–342 
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
• Positive tester probe 
Gray “1”
• Negative tester probe 
Black “2”
12
Gy B