Chapter 22 Basic Electrical Tests 339
Trial-and-Error Approach
In the past, when electrical systems were much
less complex, a technician might have been able to get
by using a trial-and-error approach. This approach
involved randomly testing or replacing system parts
until the problem was found. Older vehicles did not
have the large number of complex electronic circuits
and components found on late-model vehicles. On
older vehicles, only a few tests or part replacements
were often needed.
Today, the trial-and-error approach is not a good
alternative. This method could take hours or days
to fi nd a simple electrical problem. With on-board
computers, vehicle sensors, actuators, and the
interaction of major circuits, a systematic approach
to problem diagnosis is essential. Never use trial
and error when trying to fi nd and correct electrical
problems.
Systematic Approach
The systematic approach to troubleshooting
involves using the theory of system operation and
logical thought processes to fi nd the source of the
problem quickly. A well-planned procedure must
be followed to fi nd the source of a malfunction.
Figure 22-2 shows a mnemonic (memory-jogging
phrase) that may help you remember the steps in
using a systematic approach to troubleshooting.
Verify the Symptoms
Check the vehicle carefully to fi nd out which
components are not working. Note any unusual
noise, blown fuses, or other conditions. Try to deter-
mine which parts might be capable of causing these
symptoms. Also, think of the parts that cannot be
causing the symptoms. Ask yourself the following
questions:
• What could be causing the specifi c symptoms?
Picture the parts in the circuit and how they
function. Mentally trace through the circuit or
use a wiring diagram to fi nd out what wires,
connections, and components are in the circuit
to fi nd potential trouble sources.
• How many components are affected? If several
components are not functioning normally, you
know that something close to the power source
is probably at fault. If only one or two sections
of the circuit are faulty, you know to begin your
tests at these sections of the circuit.
• Is the problem always present, or does it only
occur some of the time? If the trouble only
occurs some of the time, the conditions causing
the problem must be simulated. For example, a
loose electrical connection might open and close
with vibration or movement. By wiggling wires
in the circuit, you can simulate the driving con-
ditions and try to make the problem occur.
• Is the problem affected by heat or cold? If the
problem only occurs on a hot day or with the
engine warmed to full operating temperature,
heat may be activating the problem. Many elec-
tronic circuits are greatly affected by heat. In
fact, too much heat can ruin an electronic com-
ponent. This might tell you which component
is at fault.
• Is the problem affected by moisture? If you dis-
cover that the trouble only occurs on a wet day,
you again have more information to use when
analyzing the source of a problem. Moisture
cannot enter a sealed electronic circuit, but it
can enter and affect wire connections and com-
ponents exposed to the environment. This type
of thinking might help you in the troubleshoot-
ing process.
Narrow down the Cause
After verifying the symptoms, narrow down the
cause to one system or circuit, if possible. This will
allow you to concentrate on the components in that
system or circuit. To narrow down the possible prob-
lem sources, use the symptoms to visualize what is
happening inside the circuit. Use your knowledge
of the specifi c system and basic rules of electricity to
determine what might be wrong.
Veronica
Verify the symptoms and problem.
Never
Narrow down the problem sources.
Touches
Test to find the cause.
Much
Make the repair.
Voltage
Verify the repair.
Figure 22-2. Use this mnemonic to remember the steps in the
troubleshooting process.