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 checkTransmission installation
Install the transmission in the reverse order of removal.
Pay attention to the following points:
Bearing and oil seal
Caution
replace the removed bearings and oil seals
with new ones.
Install the driveshaft left bearing oil seal into the
retainer using the special tool.
...
Fuel mesh filter inspection and cleaning
Inspect the fuel mesh filter in the following procedures:
remove the fuel mesh filter. Refer to “fuel pump disassembly and
assembly” .
If the fuel mesh filter is clogged with foreign particles,
it hinders smooth gasoline flow resulting in loss of
engine power. Such a filter ...
Self-diagnosis function
The self-diagnosis function is incorporated in the ecm. The function has two
modes, “user mode” and “dealer mode”.
The user can only be notified by the lcd (display) panel and led (fi indicator
light). To check the function of the
individual fi system devices, the dealer mode is provided. In ...