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 coolant solution
Use engine coolant that is com·
patible with an aluminum radiator,
mixed with distilled water at a
50:50 mixture ratio for engine
coolant solution. An engine coolant
mixture other than 50:50 can
affect cooling efficiency or rust
inhibiting performance.
Engine coolant
Engine coolant should b ...
Idle speed
Adjust the engine idle speed periodically on the engine at normal operating
temperature.
To adjust the idle speed:
Lift the fuel tank by referring to
the air cleaner section.
Start the engine and warm it
up by running at idling speed
for 10 minutes in summer
(where ambie ...
Cylinder inspection
Refer to “engine top side disassembly” .
Refer to “engine top side assembly” .
Cylinder distortion
Check the gasket surface of the cylinder for distortion.
Use a straightedge and thickness gauge. Take clearance
readings at several places. If any reading exceeds the
service limit, replace t ...