Yamaha YZ250F(E) Owner's Service Manual page 306

TIP
Make sure that the machine is completely cold before checking the coolant temperature sensor.
Fault code
Symptom
Fail-safe system
Diagnostic code No.
Diagnostic tool display
Procedure
Or- Probable cause of malfunc-
der tion and check
1 Connection of coolant tem-
perature sensor 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).
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).
3 Wire harness continuity.
4 Mounted condition of coolant
temperature sensor.
Check for looseness or
pinching.
Check the mounted condition
for correctness.
5 Defective coolant tempera-
ture sensor.
6 Faulty ECU
21
Coolant temperature sensor: open or short circuit detected.
Able to start engine
Able to drive vehicle
06
Displays the coolant temperature.
Compare the actually measured coolant temperature with the
Yamaha diagnostic tool display value.
Maintenance job
Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.
Improperly connected 
Connect the coupler secure-
ly, or repair/replace the wire
harness.
Open or short circuit  Re-
place the wire harness.
Between coolant temperature
sensor coupler and ECU cou-
pler.
green/white–green/white
black/blue–black/blue
Improperly mounted sensor
 Remount or replace the
sensor.
Execute the diagnostic mode.
(Code No. 06)
When the machine is cold,
displayed temperature is
close to the ambient temper-
ature.
Improper display  Replace
the coolant temperature sen-
sor.
Replace the ECU.
8-20
FUEL INJECTION SYSTEM
Reinstatement method
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.
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.
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.
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.
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.