Basic Diagnostic Procedure
1. Basic Diagnostic Procedure
A: BASIC PROCEDURES
1. GENERAL DESCRIPTION
The most important purpose of diagnostics is to
quickly determine which part is malfunctioning, to
save time and labor.
2. IDENTIFICATION OF TROUBLE SYMP-
Determine what the problem is based on the symp-
3. PROBABLE CAUSE OF TROUBLE
Look at the wiring diagram and check the system’s
circuit. Then check the switch, relay, fuse, ground,
4. LOCATION AND REPAIR OF TROUBLE
1) Using the diagnostics, narrow down the causes.
2) If necessary, use a voltmeter, ohmmeter, etc.
3) Before replacing certain component parts
(switch, relay, etc.), check the power supply,
ground, for open wiring harness, poor connectors,
etc. If no problem is encountered, check the com-
5. SYSTEM OPERATION CHECK
After repairing, ensure that the system operates
B: BASIC INSPECTION
1. VOLTAGE MEASUREMENT
1) Using a voltmeter, connect the negative lead to a
good ground point or negative battery terminal and
the positive lead to the connector or component ter-
2) Contact the positive lead of the voltmeter on
connector (A). The voltmeter will indicate a voltage.
3) Touch connector (B) with the positive probe. The
voltmeter will indicate no voltage.
4) With the test set-up held as it is, turn the switch
to ON. The voltmeter will indicate a voltage and, at
the same time, the light will illuminate.
5) The circuit is in good order. If a problem such as
a light failing to illuminate occurs, use the proce-
dures outlined above to track down the malfunc-
2. CIRCUIT CONTINUITY CHECKS
1) Disconnect the battery terminal or connector so
there is no voltage between the check points.
Contact the two leads of an ohmmeter to each of
the check points.
If the circuit has diodes, reverse the two leads and
2) Use an ohmmeter to check for diode continuity.
When contacting the negative lead to the diode
positive side and the positive lead to the negative
side, there should be continuity.
When contacting the two leads in reverse, there
should be no continuity.
3) The symbol “ — ” indicates that continuity
exists between two points or terminals. For exam-
ple, when a switch position is at “3”, continuity ex-
ists among terminals 1, 3 and 6, as shown in the
Continuity No continuity
Ter m i na l
asieps.book 3 ページ ２０１２年８月１６日 木曜日 午前９時６分