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Chapterhaptehapter
22TestsElectrical
After studying this chapter, you will be able to:
Use a systematic approach to fi nd and correct
electrical problems.
Explain causes of basic circuit problems given
their symptoms.
Use testing devices to check component
operation.
Use a multimeter to measure circuit voltage,
voltage drop, resistance, and amperage.
Test basic electric and electronic components.
Basic circuit testing skills are essential to
today’s automotive technicians. Knowing how
to analyze circuit problems and use basic test
instruments are fundamental skills. This chapter
introduces basic circuit problems, explains their
causes, and summarizes the tests needed to find
and correct malfunctions.
Basic Circuit Problems
Almost all electrical and electronic problems are
caused by something in the circuit that increases or
decreases current, resistance, or voltage. For exam-
ple, a broken wire could stop or decrease current,
or a charging system problem could increase output
voltage and current.
Unfortunately, when a basic circuit problem
occurs in a complex circuit, such as a computer con-
trol system, it may not seem so simple. For example,
a poor electrical connection in a feed wire to a sensor
can cause a false signal to return to the computer.
The computer, reacting to this signal, might then
alter the operation of the fuel injection system, emis-
sion control system, or ignition system. A technician
might think that any of these systems or the com-
puter itself is at fault. Several systems may appear to
have a problem. In reality, all of the problem symp-
toms are caused by a poor electrical connection in
one wire.
As you can see, it is important to keep an open
mind when diagnosing electrical problems. If ana-
lyzed properly, problems can usually be found and
corrected easily.
Electrical Diagnosis and Repair
Electrical diagnosis involves using a logical
sequence of steps to fi nd the source of an electri-
cal problem. Before you begin troubleshooting,
you should verify the symptoms and problem to
be sure that the customer has described the trouble
accurately. Frequently, the vehicle owner or service
writer may not completely describe what is wrong
with the vehicle. Verifying the problem may give
you added information when determining what to
do next. See Figure 22-1.
Basic
Figure 22-1. Verify the problem before you begin the
troubleshooting process.
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