Yamaha YZ250FX 2021, Owner'S Service Manual

Page: 317 / 378

FUEL INJECTION SYSTEM
8-30
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.
Start switch to ON (main relay
ON), and then check the condi-
tion 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
Start switch to ON (main relay
ON), and then check the condi-
tion 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.
Start switch to ON (main relay
ON), and then check the condi-
tion 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.
Start switch to ON (main relay
ON), and then check the condi-
tion 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.