Yamaha YZ250FX 2021, Owner'S Service Manual

Page: 310 / 378

FUEL INJECTION SYSTEM
8-23
EAM30286
TROUBLESHOOTING DETAILS (FAULT CODE)
This section describes the measures per fault code number displayed on the Yamaha diagnostic tool.
Check and service the items or components that are the probable cause of the malfunction following
the order given.
After the check and service of the malfunctioning part have been completed, delete the fault codes dis-
played on the Yamaha diagnostic tool according to the reinstatement method.
Fault code No.:
Fault code number displayed on the Yamaha diagnostic tool when the engine failed to work normally.
Diagnostic code No.:
Diagnostic code number to be used when the diagnostic mode is operated. Refer to “DIAGNOSTIC
CODE: SENSOR OPERATION TABLE” on page 9-12.
Parts connected to the ECU
The following parts are connected to the ECU.
When checking for a power short circuit, the couplers must be disconnected from all of the following
parts beforehand.
Fault code No. 12
• Crankshaft position sensor • Intake air pressure sensor
• Fuel injector • Coolant temperature sensor
• Ignition coil • Intake air temperature sensor
• Throttle position sensor
Fault code No. 12
Item
Crankshaft position sensor: no normal signals are received from
the crankshaft position sensor.
Fail-safe system
Unable to start engine
Unable to drive vehicle
Diagnostic code No. —
Diagnostic tool display —
Procedure —
Item
Probable cause of malfunc-
tion and check
Maintenance job
Confirmation of service com-
pletion
1 Connection of crankshaft posi-
tion 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).
Improperly connected

Con-
nect the coupler securely, or
repair/replace the wire harness.
Crank the engine, 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.
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.
Crank the engine, 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.