Yamaha WR450FN 2022 Owner's Service Manual page 338

Fault code No.
Item
1 Mounted condition of throttle
position sensor.
Check for looseness or pinch-
ing.
Check the mounted condition
for correctness.
2 Defective throttle position sen-
sor.
3 Faulty ECU.
4 Delete the fault code.
Fault code No. 21
TIP
• Make sure that the machine is completely cold before checking the coolant temperature sensor.
• Before troubleshooting, disconnect the starter motor lead from the starter relay.
Fault code No.
Item
Fail-safe system
Diagnostic code No.
Diagnostic tool display
Procedure
Probable cause of malfunc-
Item
tion and check
1 Connection of coolant tempera-
ture sensor 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).
16
Throttle position sensor: stuck throttle position sensor is detected.
Improperly mounted sensor 
Remount or replace the sensor.
Refer to "ADJUSTING THE
THROTTLE POSITION SEN-
SOR" on page 7-8.
Execute the diagnostic mode.
(Code No. 01)
When the throttle is fully closed,
11–14 displays.
When the throttle is fully
opened, 86–92 displays.
Incorrect display range 
Replace the throttle position
sensor.
Replace the ECU.
Confirm that the fault code has
a condition of "Recovered"
using the Yamaha diagnostic
tool, and then delete the fault
code.
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  Con-
nect the coupler securely, or
repair/replace the wire harness.
8-39
FUEL INJECTION SYSTEM
Push the start switch (main
relay ON) and open and close
the throttle several times.
Check the condition of the fault
code using the malfunction
mode of the Yamaha diagnostic
tool.
Condition is "Recovered"  Go
to item 4 and finish the service.
Condition is "Detected"  Go to
item 2.
Push the start switch (main
relay ON) and open and close
the throttle several times.
Check the condition of the fault
code using the malfunction
mode of the Yamaha diagnostic
tool.
Condition is "Recovered"  Go
to item 4 and finish the service.
Condition is "Detected"  Go to
item 3.
Service is finished.
Confirmation of service com-
pletion
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 2.