Subaru 2009 IMPREZA, Service Manual

Page: 3422 / 3619

WI-3
Basic Diagnostic Procedure
WIRING SYSTEM
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 SYMPTOM
Determine what the problem is based on the symp-
tom.
3. PROBABLE CAUSE OF TROUBLE
Look at the wiring diagram and check the system’s
circuit. Then check the switch, relay, fuse, ground,
etc.
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-
ponent parts.
5. SYSTEM OPERATION CHECK
After repairing, ensure that the system operates
properly.
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-
minal.
2) Touch connector (A) with the positive probe of
the volt meter. 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-
tion.
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
check again.
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.
To power
Fuse
supply
Switch
Light
V
(A)
(B)
WI-02739
Continuity No continuity
WI-02740