Possible causes for the open circuit are as follows. As the cause can exist in the connector/coupler or terminal, they need to be checked carefully.
When checking system circuits including an electronic control unit such as ecm, etc., It is important to perform careful check, starting with items which are easier to check.

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Check each terminal visually for poor contact (possibly caused by dirt, corrosion, rust, entry of foreign object, etc.). At the same time, check to make sure that each terminal is fully inserted in the coupler and locked.
If contact tension is not enough, rectify the contact to increase tension or replace. The terminals must be clean and free of any foreign material which could impede proper terminal contact.

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Locate abnormality, if any.

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Battery
Continuity checkEngine bottom side disassembly
Note
the crankcase must be separated to service
the crankshaft and conrod.
Remove the engine assembly from the frame. Refer to “engine assembly
removal” .
Remove the engine top side (1). Refer to “engine top side disassembly”
.
Crankcase breather (pcv) cover
R ...
DTC “c91” (p0500): vehicle speed sensor
circuit malfunction
Detected condition and possible cause
Detected condition
Possible cause
Speedometer does not receive signal from the vehicle
speed sensor for more than 6 sec. When the motorcycle is
running. Ecm does not receive signal from the vehicle
speed sensor for more than ...
Fi system troubleshooting
Customer complaint analysis
Record details of the problem (failure, complaint) and how it occurred as
described by the customer. For this purpose,
use of such an inspection form such as following will facilitate collecting
information to the point required for proper
analysis and diagnosis.
...