Yamaha WR250F 2021 - Page 341

FUEL INJECTION SYSTEM
8-40
2 Connection of wire harness
ECU coupler.
Check the locking condition of
the coupler.
Disconnect the coupler, and
check the pins (for bent or bro-
ken terminals and locking condi-
tion of the pins).
Improperly connected  Con-
nect the coupler securely, or
repair/replace the wire harness.
Push the start switch (main
relay ON), and then check the
condition of the fault code using
the malfunction mode of the
Yamaha diagnostic tool.
Condition is “Recovered”  Go
to item 7 and finish the service.
Condition is “Detected”  Go to
item 3.
3 Wire harness continuity. Open or short circuit  Replace
the wire harness.
Between coolant temperature
sensor coupler and ECU cou-
pler.
green/white–green/white
black/blue–black/blue
Push the start switch (main
relay ON), and then check the
condition of the fault code using
the malfunction mode of the
Yamaha diagnostic tool.
Condition is “Recovered”  Go
to item 7 and finish the service.
Condition is “Detected”  Go to
item 4.
4 Mounted condition of coolant
temperature sensor.
Check for looseness or pinch-
ing.
Check the mounted position for
correctness.
Improperly mounted sensor 
Remount or replace the sensor.
Push the start switch (main
relay ON), and then check the
condition of the fault code using
the malfunction mode of the
Yamaha diagnostic tool.
Condition is “Recovered”  Go
to item 7 and finish the service.
Condition is “Detected”  Go to
item 5.
5 Defective coolant temperature
sensor.
Execute the diagnostic mode.
(Code No. 06)
When the machine is cold, dis-
played temperature is close to
the ambient temperature.
Improper display  Replace the
coolant temperature sensor.
Refer to “RADIATOR” on page
6-2.
Push the start switch (main
relay ON), and then check the
condition of the fault code using
the malfunction mode of the
Yamaha diagnostic tool.
Condition is “Recovered”  Go
to item 7 and finish the service.
Condition is “Detected”  Go to
item 6.
6 Faulty ECU. Replace the ECU. Service is finished.
7 Delete the fault code. Confirm that the fault code has
a condition of “Recovered”
using the Yamaha diagnostic
tool, and then delete the fault
code.
Fault code No. 21
Item Coolant temperature sensor: open or short circuit detected.