4-6 FI SYSTEM DIAGNOSIS
• Before measuring voltage at each terminal, check to make
sure that battery voltage is 11 V or higher. Terminal voltage
check with a low voltage battery will lead to erroneous diagno-
sis.
• Never connect any tester (voltmeter, ohmmeter, or whatever)
to the electronic unit when its coupler is disconnected.
Otherwise, damage to electronic unit may result.
• Never connect an ohmmeter to the electronic unit with its cou-
pler connected. If attempted, damage to ECM or sensors may
result.
• Be sure to use a specified voltmeter/ohmmeter. Otherwise,
accurate measurements may not be obtained and personal
injury may result.
ELECTRICAL CIRCUIT INSPECTION
PROCEDURE
While there are various methods for electrical circuit inspection,
described here is a general method to check for open and short
circuit using an ohmmeter and a voltmeter.
OPEN CIRCUIT CHECK
Possible causes for the open circuits are as follows. As the
cause can exist in the connector/coupler or terminal, they need
to be checked carefully.
• Loose connection of connector/coupler.
• Poor contact of terminal (due to dirt, corrosion or rust, poor
contact tension, entry of foreign object etc.).
• Wire harness being open.
• Poor terminal-to-wire connection.
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.
• Disconnect the negative cable from the battery.
• Check each connector/coupler at both ends of the circuit
being checked for loose connection. Also check for condition
of the coupler lock if equipped.
1 Sensor
2 ECM
*1 Check for loose connection.
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