Mitsubishi Galant 9G. Manual — part 318

HOW TO DIAGNOSE

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GENERAL <ELECTRICAL>

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HOW TO DIAGNOSE

HOW TO DIAGNOSE

M1001004300086

The most important point in troubleshooting is to
determine "Probable Cause." Once the probable
causes are determined, parts to be checked can be
limited to those associated with such probable
causes. The determination of the probable causes
must be based on a theory and be supported by facts
and must not be based on intuition only.

TROUBLESHOOTING STEPS

M1001004400049

If an attempt is made to solve a problem without going through correct steps for troubleshooting, the symp-
toms could become more complicated, resulting in failure to determine the causes correctly and making
incorrect repairs. The four steps below should be followed in troubleshooting.

INFORMATION FOR DIAGNOSIS

M1001004500132

This manual contains the harness diagrams as well as the individual circuit drawings, operational explana-
tions, and troubleshooting hints for each component. The information is presented in the following manner:
1. Connector diagrams show the connector

positions, etc., on the actual vehicle as well as the
harness path.

2. Circuit diagrams show the configuration of the

circuit with all switches in their normal positions.

3. Operational explanations include circuit drawings

of current flow when the switch is operated and
how the component reacts.

ACX00915

3

Checking of Parts Associated with
Probable Causes and Determination
of Faulty Parts

2 Determination of Probable Causes

4 Repair and Confirmation

Observe the symptom carefully. Check if there are also
other problems.

In determining the probable causes, it is necessary to
study the wiring diagram to understand the circuit as a
system. Knowledge of switches, relays and other parts is
necessary for accurate analysis. The causes of similar
problems in the past must be taken into account.

Troubleshooting is carried out by making step-by-step
checks until the cause is found.

After the problems are corrected, be sure to check that the
system operates correctly. Also check that new problems
have not been caused by the repair.

AC

1 Observation of Problem Symptoms

HOW TO DIAGNOSE

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4. Troubleshooting hints include numerous

examples of problems which might occur, traced
backward in a common-sense manner to the
origin of the trouble. Problems whose origins may
not be found in this manner are pursued through
the various system circuits.

NOTE: Components of MFI, ETACS, etc. with ECU do not include 3 and 4 above. For this information, refer
to a relevant group which includes details of these components.

INSPECTION

M1001004600139

1. Sight and sound checks

Check relay operation, blower motor rotation, light
illumination, etc. Listen for a "click" when some relay covers
are pushed down.

2. Simple checks

For example, if a headlight does not come on and a faulty
fuse or poor grounding is suspected, replace the fuse with a
new one. Or use a jumper wire to ground the light to the
body. Determine which part(s) is/are responsible for the
problem.

3. Checking with instruments

Use an appropriate instrument in an adequate range and
read the indication correctly.

ACX00936 AB

CLICK

ACX00937

ACX00938AB

SELECTOR KNOB

POINTER

HOW TO DIAGNOSE

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INSPECTION INSTRUMENTS

M1001004700040

For inspection, use the following instruments:

CAUTION

Never use a test light for checking ECU-related circuits or
ECUs.
1. Test light

A test light consists of a 12V bulb and lead wires. It is used
to check voltages or short circuits.

2. Self-powered test light

A self-powered test light consists of a bulb, battery and lead
wires connected in series. It is used to check continuity or
grounding.

CAUTION

Never use a jumper wire to connect a power supply
directly to a load.
3. Jumper wire

A jumper wire is used to close an open circuit.

4. Voltmeter

A voltmeter is used to measure the circuit voltage. Normally,
the positive (red lead) probe is applied to the point of voltage
measurement and the negative (black lead) probe to the
body ground. Use a digital voltmeter to check for voltage
drop before or after a component.

ACX00939

ACX00940

ACX00941

ACX00942 AB

RED LEAD WIRE

POWER LINE

BLACK LEAD WIRE

GROUND

HOW TO DIAGNOSE

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5. Ohmmeter

An ohmmeter is used to check continuity or measure
resistance of a switch or coil. If the measuring range has
been changed, the zero point must be adjusted before
measurement.

CHECKING FUSES

M1001005000044

A blade type fuse has test taps provided to allow checking of
the fuse itself without removing it from the fuse block. The fuse
is okay if the test light comes on when its one lead is connected
to the test taps (one at a time) and the other lead is grounded.
Remember to turn the ignition switch to ON to ensure all cir-
cuits are live.

CAUTIONS IN EVENT OF BLOWN FUSE

When a fuse is blown, there are two probable causes. One is
that it is blown due to flow of current exceeding its rating. The
other is that it is blown due to repeated on/off current flowing
through it. Which of the two causes is responsible can be easily
determined by visual check as described below.
1. Fuse blown due to current exceeding rating

The illustration shows the state of a fuse blown due to this
cause. In this case, do not replace the fuse with a new one
hastily since a current heavy enough to blow the fuse has
flowed through it. First, check the circuit for shorts and check
for abnormal electric parts. After correcting shorts or
replacing parts, use only a fuse of the same capacity as a
replacement. Never use a fuse of larger capacity than the
original fuse. If a larger capacity fuse is used, electric parts
or wiring could be damaged, or could start a fire.

2. Fuse blown due to repeated turning current on and off

The illustration shows the state of a fuse blown due to
repeated current on/off. Normally, this type of problem
occurs after a fairly long period of use and is less frequent
than above. In this case, simply replace with a new fuse of
the same capacity.

ACX00943

ACX00951AB

FUSE BLOCK

TEST TAPS

ACX00952 AB

STATE OF FUSE BLOWN DUE TO
OVERCURRENT

ACX00953 AB

STATE OF FUSE BLOWN DUE TO
THERMAL FATIGUE