Yamaha YXR70FX Service Manual page 290

Fault code No. 37
Diagnostic code No. d54
Order Item/components and probable
cause
1 Backup fuse is blown.
2 Throttle valve does not fully close.
3 ISC valve is stuck fully open due to
disconnected ISC unit hose or cou-
pler. (High engine idle speed is
detected with the ISC valve stuck
fully open even though signals for
the valve to close are continuously
being transmitted by the ECU.)
4 ISC valve is not moving correctly.
FUEL INJECTION SYSTEM
Symptom Engine speed is high when the engine is idling.
ISC valve
Check or maintenance job
• Check the backup fuse.
Refer to "CHECKING THE
FUSES" in chapter 3.
• Check the throttle body.
Refer to "THROTTLE BODY".
• Check the throttle cables.
Refer to "ADJUSTING THE
THROTTLE CABLE" in chapter
3.
• Check that the ISC unit coupler
is not disconnected.
• The ISC valve is stuck fully open
if it does not operate when the
main switch is turned "OFF".
(Touch the ISC unit with your
hand and check if it is vibrating
to confirm if the ISC valve is
operating.)
• Execute the diagnostic mode.
(Code No.d54)
• After the ISC valve is fully
closed, it opens to the standby
opening position when the
engine is started. This operation
takes approximately 12 seconds.
Start the engine. If the error
recurs, replace the throttle body
assembly.
6 - 20
FI
Reinstatement
method
ISC valve
returns to its
original position
by turning the
main switch to
"ON" and back
to "OFF".
Reinstated if the
engine idle
speed is within
specification
after starting the
engine.