Yamaha 2004 YP400 Service Manual page 320

Fault code No. 37
Used diagnostic code No. 54 (ISC (idle speed control) valve)
Order Inspection operation item and
probable cause
1 Incorrect speed sensor signal
2 Throttle valve does not fully close
3 ISC (idle speed control) valve
stuck fully open
4 ISC (idle speed control) valve not
moving correctly
Fault code No. 39
Used diagnostic code No. 36 (fuel injector)
Order Inspection operation item and
probable cause
1 Connected condition of connector
Inspect the coupler for any pins
that may have pulled out.
Check the locking condition of the
coupler.
2 Open or short circuit in lead wire.
3 Defective fuel injector
FUEL INJECTION SYSTEM
Symptom Engine speed is high when the engine is idling.
Operation item and countermeasure
Check the speed sensor.
Check the speed sensor leads.
Check the speed sensor coupler.
Check the throttle body.
Refer to "THROTTLE BODY AND FUEL INJEC-
TOR".
Check the throttle cables.
Refer to "ADJUSTING THE THROTTLE CABLE
FREE PLAY" in chapter 3.
The ISC (idle speed control) valve is stuck fully open
if it does not operate when the main switch is set to
OFF.
(Touch the ISC (idle speed control) valve unit with
your hand and check if it is vibrating to confirm if the
ISC (idle speed control) valve is operating.)
NOTE:
Do not remove the ISC (idle speed control) valve
unit.
Execute the diagnostic mode (code No. 54)
After the ISC (idle speed control) valve is fully
closed, it opens until it is at the standby opening
position when the engine is started. This operation
takes approximately 12 seconds until it is com-
pleted. Start the engine. If the error recurs, replace
the throttle body assembly.
Symptom Fuel injector open or short circuit is detected.
Operation item and countermeasure
If there is a malfunction, repair it and connect it
securely.
Fuel injector coupler – orange/black
Main wiring harness ECU coupler
Sub-wire harness coupler
Repair or replace if there is an open or short circuit.
Between fuel injector coupler and ECU coupler/main
harness
orange/black – orange/black
Execute the diagnostic mode (code No. 36)
Replace if defective.
7 - 19
FI
Reinstatement
method
Reinstated if the
engine idle speed
is within specifica-
tion after starting
the engine.
Reinstatement
method
Reinstated by
starting the engine.