Yamaha YZ 2018 Series, Owner'S Service Manual, Page: 328 / 402

FUEL INJECTION SYSTEM
8-29
TROUBLESHOOTING DETAILS
This section describes the measures per fault code number displayed on the diagnostic tool. Check
and service the items or components that are the probable cause of the malfunction following the or-
der given.
After the check and service of the malfunctioning part have been completed, reset the diagnostic tool
display according to the reinstatement method.
Fault code No.:
Fault code number displayed on the diagnostic tool when the engine failed to work normally.
Diagnostic code No.:
Diagnostic code number to be used when the diagnostic mode is operated.
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
completion
1 Connection of crankshaft po-
sition sensor coupler.
Check the locking condition
of the coupler.
Disconnect the coupler and
check the pins (bent or bro-
ken terminals and locking
condition of the pins). Improperly connected

Connect the coupler securely
or repair/replace the wire har-
ness.
Crank the engine.
Fault code number is not dis-
played

Service is finished.
Fault code number is dis-
played

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 (bent or bro-
ken terminals and locking
condition of the pins). Improperly connected

Connect the coupler securely
or repair/replace the wire har-
ness.
Crank the engine.
Fault code number is not dis-
played

Service is finished.
Fault code number is dis-
played

Go to item 3.
3 Wire harness continuity. Open or short circuit

Re-
place the wire harness.
Between the crankshaft posi-
tion sensor coupler and ECU
coupler.
black/blue–black/blue
gray–gray
Crank the engine.
Fault code number is not dis-
played

Service is finished.
Fault code number is dis-
played

Go to item 4.
4 Installed condition of crank-
shaft position sensor.
Check for looseness or
pinching.
Check the gap between the
crankshaft position sensor
and the pickup rotor. Improperly installed sensor

Reinstall or replace the
sensor.
Refer to “GENERATOR AND
STARTER CLUTCH” on
page 5-59.
Crank the engine.
Fault code number is not dis-
played

Service is finished.
Fault code number is dis-
played

Go to item 5.