Yamaha MTN850-A 2017 Service Manual page 435

Fault code No. P0638
Fault code No.
Item
Fail-safe system
Diagnostic code No.
Tool display
Procedure
Probable cause of malfunc-
Item
tion and check
1 Connection of throttle servo
motor coupler.
Check the locking condition of
the coupler.
Disconnect the coupler and
check the pins (bent or broken
terminals and locking condition
of the pins).
2 Connection of wire harness
ECU coupler.
Disconnect the coupler and
check the pins (bent or broken
terminals and locking condition
of the pins).
3 Check the electronic throttle
valve fuse.
4 Wire harness continuity.
5 Defective throttle servo motor.
P0638
YCC-T drive system: malfunction detected.
Able/Unable to start engine
Able/Unable to drive vehicle
—
—
—
Maintenance job
Improperly connected  Con-
nect the coupler securely or
replace the wire harness.
Improperly connected  Con-
nect the coupler securely or
replace the wire harness.
Blown fuse  Replace the elec-
tronic throttle valve fuse.
Open or short circuit  Replace
the wire harness.
Between throttle servo motor
coupler and ECU coupler.
yellow/red–yellow/red
yellow/white–yellow/white
Between ECU coupler and fuse
box (electronic throttle valve
fuse).
red/white–red/white
Check the throttle servo motor.
Replace the throttle bodies if
defective.
Refer to "CHECKING THE
THROTTLE SERVO MOTOR"
on page 8-171.
8-78
FUEL INJECTION SYSTEM
Confirmation of service com-
Turn the main switch to "ON",
and then check the condition of
the fault code using the mal-
function mode of the Yamaha
diagnostic tool.
Condition is "Recovered"  Go
to item 8 and finish the service.
Condition is "Detected"  Go to
item 2.
Turn the main switch to "ON",
and then check the condition of
the fault code using the mal-
function mode of the Yamaha
diagnostic tool.
Condition is "Recovered"  Go
to item 8 and finish the service.
Condition is "Detected"  Go to
item 3.
Turn the main switch to "ON",
and then check the condition of
the fault code using the mal-
function mode of the Yamaha
diagnostic tool.
Condition is "Recovered"  Go
to item 8 and finish the service.
Condition is "Detected"  Go to
item 4.
Turn the main switch to "ON",
and then check the condition of
the fault code using the mal-
function mode of the Yamaha
diagnostic tool.
Condition is "Recovered"  Go
to item 8 and finish the service.
Condition is "Detected"  Go to
item 5.
Turn the main switch to "ON",
and then check the condition of
the fault code using the mal-
function mode of the Yamaha
diagnostic tool.
Condition is "Recovered"  Go
to item 8 and finish the service.
Condition is "Detected"  Go to
item 6.
pletion