Jeep 1987 Wrangler Workshop Manual page 1771

B. SPECIFIC DEFINITIONS AND EXAMPLES
STEP
1: V E R I F Y T H E C O M P L A I N T . If a
customer complains of a specific problem,
the first thing you should do is find out if the
problem really exists. Let's say the customer
complains the horn doesn't work. You should
then verify the complaint by pushing down
the horn ring and listen for the beep. This
action of depressing the horn ring is called an
operational check. When you perform
operational checks you are looking for
symptoms; both positive and negative.
Positive Symptoms
are symptoms which are
correct. For example, the radio plays when
the radio switch is turned on.
Negative Symptoms
are symptoms which are
incorrect. For example, the horn does not
blow when the horn ring is depressed.
If you are in doubt as to how a circuit
operates, refer to the schematic and circuit
operation. The layout of the schematic
simplifies all circuit operations. Circuits can
be traced in a matter of seconds.
IGNITION
SWITCH
IGNITION
ON
RELAY
B
BATTERY
< < <
X> F18 \ ) F17 X> F15
REAR
WINDOW
DEFOGGER
CIRCUIT
BACK-UP
LAMP
SWITCH
A
Ci
IC
CT.
BACK-UP
LAMPS
D
Sometimes the problem may be intermittent
(momentarily present and not present). If so,
road test vehicle, and if possible, have the
customer show you w h a t happens. Try to
duplicate the conditions in order to make the
trouble appear. You cannot find a problem if
everything works normally. When t h e
problem occurs, note the symptoms.
Remember! Make sure of both the positive
and negative symptoms. They are both
important.
STEP
2: D E T E R M I N E RELATED
SYMPTOMS.
Determining related symptoms is a very
important step. It will save you much time in
the long run. In order to get additional
information about where the problem exists,
related symptoms are found by conducting
operational checks on circuits which are
connected to the problem circuit. Operational
checks are made without the use of test
equipment. Your most important tool will be
the schematic. For example, refer to Fig l.
If the customer complaint was that t h e Back
Up Lamps didn't work, you would trace the
circuit starting at ground until you come to
the first common point [A]. As can be seen, the
Windshield Wiper and Seat Belt Timer
circuits are also connected to point A.
Therefore, you should conduct operational
checks on these circuits to see if they operate.
If they do (positive symptoms), you should
then proceed to Step 3 in the troubleshooting
procedure.
C
WINDSHIELD
WIPER/WASHER
CIRCUIT
SEAT
BELT
TIMER
CIRCUIT
Fig. I
If the circuit did not operate, you would then
continue tracing the circuit toward the
Battery until you reach the next common
point IB]. The A/C and Rear Window Defogger
circuits are connected to pont B. Therefore,
you should check to see if they operate. If they
do, you would then proceed to Step 3.
STEP
3; ANALYZE T H E S Y M P T O M S .
1. Localizing the Trouble:
After conducting operational checks (Step 2),
the trouble will always lie between a check
which resulted in negative symptoms, and a
check which resulted in a positive
symptom.
Consider the following examples (refer to Fig
I):
EXAMPLE 1: If the Back Up Lamps did not
operate, but the Windshield
Wiper did, the trouble would lie
between point A and ground at
the Back Up Lamps.
EXAMPLE 2: If the Back Up Lamps,
Windshield Wiper, and Seat Belt
Timer didn't operate, but the A/C
and Rear Window Defogger did,
the trouble would lie between
point B and ground.
In Example 1 above, the trouble would be an open,
since a short would have caused Fuse F15 to open,
and the Windshield Wiper and Seat Belt Timer
would not operate.
In Example 2 above, the trouble may be a short.
Fuse F15 may have opened due to a short in either
the Back Up Lamps, Windshield Wiper/Washer,
or Seat Belt Timer circuits.
Electrical problems are mainly caused by either
open or short circuits.
2. Open Circuits.
An open circuit is like an open switch. It
interrupts the flow of current. An open circuit
has an infinite resistance; therefore, no
current will flow. Open circuits can be caused
by broken wires, parts going bad, loose
connections, (like ground screws), and by
foreign matter being stuck between contacts.
3. Short Circuit.
A short circuit allows excessive current to
flow in a circuit beacuse of the resistance of
the circuit going to zero ohms, which usually *
results in a blown fuse.
4. Intermittent Open Circuits.
This condition can be caused by a piece of dirt
becoming momentarily caught between two
contacts. In the case of rubber disconnects,
excessive rubber could be spilled over into the
pins. Other causes could be loose connectors,
resulting in poor terminal contact.
5. Intermittent Short Circuits.
This condition can be caused by a frayed wire
momentarily touching another wire. A slight
bump can cause contact to be made, then
broken.
6. Symptoms of Short Circuits [refer to Fig. I J:
A short between points C and D will cause
Fuse F15 to blow (open). Therefore, the Back
Up Lamps, Windshield Wiper/Washer, and
Seat Belt Timer circuits will not work.
7. Determine a Plan.
When analyzing symptoms, there are three
things to consider:
a. W h a t goes wrong most of the time? Some
parts receive more use than others and
therefore wear out sooner. Other parts are
subjected to corrosion such as grounds,
while others are just natural trouble spots.
b. Check parts which are closest to you. This
will save time. Simple tests should be made
first.
c. How difficult the parts are to get to in order
to perform checks on them determines the
order in which they are checked. Leave the
more difficult places until last. There is no
substitute for common sense.
8. Test Equipment.
In developing a strategy to isolate the
problem, 3 meters and jumper wires could be
used (see following page). Above each meter is
a short explaination of their purpose, and how
each meter is used.
Introduction
3
Introduction