Honda SH125 Manual page 318

IGNITION SYSTEM
TROUBLESHOOTING
Inspect the following before diagnosing the system.
-
Faulty spark plug
-
Loose spark plug cap or spark plug wire connection
- Water got into the spark plug cap (leaking the ignition coil secondary voltage)
"Initial voltage" of the ignition primary coil is the battery voltage with the ignition switch turned to ON (The engine is not
cranked
by
the starter motor).
NO SPARK AT PLUG
Ignition coil
primary volt-
age
Crankshaft
position
(CKP) sensor
Unusual condition
No initial voltage with ignition
switch turned to
ON
(Other electri-
cal components are normal)
Initial voltage is normal, but it drops
down t o 2
-
4 V while cranking the
engine.
Initial voltage is normal, but no peak
voltage while cranking the engine.
Initial voltage is normal, but peak
voltage is lower than standard
value.
Initial and peak voltage are normal,
but no spark jumps at plug.
Peak voltage low
No peak voltage.
Probable cause (Check in numerical order)
1 . An open circuit in BlacWwhite wire between the igni-
tion coil and engine stop relay.
2. An open circuit or loose connection in engine stop
relay related circuit or faulty engine stop relay.
3. Loose or poor contact of the ignition coil primary wire
terminal, or an open circuit in primary coil. (Check at
the ECM connector.)
4. Faulty ECM (when the initial voltage
is
normal with the
ECM connector disconnected).
1. Incorrect peak voltage adaptor connections.
2. Undercharged battery.
3. No voltage between the BlacWwhite
(+)
and body
ground
(-1
at the ECM connector or loosen ECM con-
n ect
0
r.
4. An open circuit or loose connection in Greedpink wire
of the ECM.
5. An open circuit or loose connection in Yellowlblue
wire between the ignition coil and ECM.
6. Short circuit in the ignition primary coil.
Z Faulty CKP sensor (measure the peak voltage).
8. Faulty ECM (when above No.1
-
7 are normal).
1. Incorrect peak voltage adaptor connections.
2. Faulty peak voltage adaptor.
3. Faulty ECM (when above No.1 and 2 are normal).
1 . The multimeter impedance is too low; below 10 MR/
DCV.
2. Cranking speed is too slow. (Battery is undercharged.)
3. The sample timing of the tester and measured pulse
were not synchronized. (System is normal if measured
voltage is over the standard voltage at least once.)
4. Faulty ignition coil.
5. Faulty ECM (when above No.1
-
4 are normal).
1. Faulty spark plug or leaking ignition coil secondary
current amDere.
2. Faulty ignit'ion coil.
1. The multimeter impedance is too low; below 10 M W
DCV.
2. Cranking speed is too slow. (Battery is undercharged.)
3. The sampling timing of the tester and measured pulse
were not synchronized. (System is normal if measured
voltage is over the standard voltage at least once.)
4. Faulty CKP sensor (when above No. 1
-
3 are normal).
1. Faulty peak voltage adaptor.
2. Faultv CKP sensor.