Yamaha RS90GTZ Service Manual page 353

Fault code No. 37
Diagnostic code No. d:54 (ISC (idle speed control) unit)
Item/components and probable cause
Order
Throttle valve does not fully close.
1
ISC valve is stuck fully open due to discon-
nected ISC unit coupler. (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
2
by the ECU.)
ISC valve is not moving correctly.
3
4 Malfunction in ECU.
Fault code No. 42
Diagnostic code No. d:07 (speed sensor)
Item/components and probable cause
Order
Connections
• Speed sensor coupler
1 • Wire harness ECU coupler
Open or short circuit in wire harness.
2
Defective speed sensor.
3
Gear for detecting snowmobile speed has
4 broken.
5 Malfunction in ECU.
FUEL INJECTION SYSTEM
Symptom Engine speed is high when the engine is idling.
Check or maintenance job
Check the throttle body.
Refer to "THROTTLE BODY".
Check the throttle cable.
Refer to "THROTTLE CABLE FREE PLAY
ADJUSTMENT" in CHAPTER 2.
Check that the ISC unit coupler is not discon-
nected.
The ISC valve is stuck fully open if it does not oper-
ate when turning the main switch off.
(Touch the ISC unit with your hand and check if it is
vibrating to confirm if the ISC valve is operating.)
TIP
Do not remove the ISC unit.
Execute the diagnostic mode (code No. 54).
After fully closing the ISC valve, it returns to full
open. This takes approximately 3 seconds.
Check the operating noise at this time.
If there is no operating noise, replace the throttle
body assembly.
Replace the ECU.
Symptom No normal signals are received from the speed sensor.
Check or maintenance job
Check the couplers for any pins that may have
pulled out.
Check the locking condition of the couplers.
If there is a malfunction, repair it and connect the
coupler securely.
Repair or replace if there is an open or short circuit.
Between the speed sensor coupler and ECU cou-
pler.
Blue – Blue
White – White
Black/Blue – Black/Blue
Execute the diagnostic mode (code No. d:07).
Replace if defective.
Refer to "SIGNAL SYSTEM" in CHAPTER 8.
Replace if defective.
Refer to "FRONT AXLE AND TRACK" in CHAP-
TER 4.
Replace the ECU.
7-26
FI
Reinstate-
ment method
ISC valve
returns to its
original posi-
tion by set-
ting the
engine stop
switch to
"RUN" and
turning the
main switch
on and off.
Reinstated if
the engine
idle speed is
within specifi-
cation after
starting the
engine.
Reinstate-
ment method
Starting the
engine, and
inputting the
snowmobile
speed sig-
nals by oper-
ating the
snowmobile
at a low
speed of
approxi-
mately 5 km/
h.