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 checkSpecial tools and equipment
Recommended service material
Note
required service material is also described in the following.
“Clutch control system components” “clutch components”
Special tool
...
Speed sensor removal and installation
Removal
Remove the left side cowling. Refer to “exterior parts removal and
installation” in section 9d .
Disconnect the speed sensor lead wire coupler (1).
Remove the speed sensor (2).
Installation
Install the speed sensor in the reverse order of removal.
Pay atte ...
Cam chain tension adjuster inspection
The cam chain tension adjuster is maintained to proper
tension automatically.
Remove the cam chain tension adjuster. Refer to “engine top side
disassembly” .
Holding the cam chain tension adjuster as shown in
the figure, compress the plunger by turning the
adjuster body unt ...