ALL ABOUT ELECTRONICS
The fundamental difference between an electrical system
circuit and an electronic circuit is the amount of electrons that
flow through the circuit. Electrical currents are generally
measured in amps while electronic currents are measured in
milliamps (.001 amps).
Electronic circuits are also based on "solid state"
components such as "transistors" and "diodes." They're called
solid state components because they have no moving parts. Solid
state electronics have revolutionized the world, and along with
it automotive ignition, fuel and emissions control systems.
Electronics are now used to regulate everything from antilock
braking and traction control to automatic transmissions and
To understand how solid state electronic devices work, we
have to go down to the atomic level. The electrical properties
of a material are determined by the number of electrons in the
outermost shell (valence ring) of its atoms. Metal atoms have
three or less electrons in the outer shell, making them good
conductors of electricity. Insulators such as glass, rubber and
most plastics, have five or more electrons in the outer shell
which inhibits the flow of electricity. But some materials have
exactly four electrons in the outermost shell. This gives them
unique electrical properties that allow the material to either
act like an insulator or a conductor under certain conditions (as
when doped with other atoms). These materials are called
semiconductors, and are the basis of solid state electronic
The age of solid state electronics actually began with the
invention of the vacuum tube, not the transistor. The glass
vacuum tubes that were once used in radios and later televisions
were really the first electronic switching devices that used
electronics rather than mechanical contacts to reroute the flow
of electrons through a circuit. Vacuum tubes are no longer used
today because they consume too much power, generate too much
heat, are bulky and fragile. They also tended to fail rather
frequently. But they laid the groundwork for the solid state
revolution that was to follow.
In 1948, Bell Laboratories made what was to become one of the
key inventions of this century: the transistor. A transistor is
essentially a switch that reroutes an electrical current
according to a voltage input. A transistor performs the same
switching function as a vacuum tube except that it does not
require a heated filament or magnetic field to switch the circuit
path. The switching function is accomplished by changing the
conductivity of the junction inside the transistor.
A transistor is made by sandwiching together three layers of
silicone or germanium crystal that have been doped to create
opposite electrical properties. When certain trace impurities
are added to either silicone or germanium crystals during their
manufacture, it alters the material's electrical properties.
Remember what we said about semiconductors having four electrons
in the outermost ring? In a pure crystal of either material, the
outer rings of the atoms link up in such a way that there aren't
any "holes" left over for extra electrons to move about (a hole
is a space in an outer orbit for an
electron to orbit). Pure silicone and germanium are actually
good insulators. But when the crystals are doped with trace
"impurities" the neat arrangement of electrons is upset. The
trace impurities (which only require about one atom in 10
million!) add just enough extra electrons or create just enough
empty holes that the material will conduct a current when a
voltage is applied. This transforms them into semiconductors.
Doping creates one of two basic types of semiconductor
materials. One is "Negative" or "N-type." To create a N-type
semiconductor material, the crystal is doped with atoms (such as
phosphorus) that have five or more electrons in their outer
valence ring. The extra electron doesn't fit into the neat
arrangement within the crystal, so a surplus of electrons is
created that gives the crystal a negative charge. The other type
of semiconductor material is the "Positive" or "P-type."
Positive semiconductors are doped with atoms (such as boron,
indium or aluminum) that have three or fewer electrons in the
outer valence ring. The missing electrons leave holes in the
crystal lattice into which electrons can move when a voltage is
applied. Thus P-type semiconductors have a positive charge.
So how does all this work together to make a
like a switch? The transistor consists of three layers of
alternating semiconductor material: either N-P-N or P-N-P. Each
layer is connected to its own electrical lead. The "in" lead is
called the "emitter," the "out" lead is called the "collector,"
and the center control lead is called the "base." The middle
base layer is the one that performs the switching function by
either allowing current to pass from the emitter or in lead to
the collector or out lead.
Current cannot move from the emitter side to the collector
side within the transistor unless voltage is also supplied to
the middle base layer. The opposite charge of the center base
layer creates a boundary across which current can't pass because
there aren't enough extra electrons (N-type) or holes (P-type) to
carry it. But when an outside voltage is applied to the base
layer, it reverses the charge and makes it conductive. The
outside voltage provides the extra electrons or holes depending
on the type of material (N-type or P-type) that are needed to
carry the current. The switch "closes" and the transistor passes
current to the opposite side.
Thus the on/off switching function of a transistor is
controlled by the application of voltage rather than opening a
set of mechanical contacts as in a conventional switch.
The same type of transistor can also be made to act like a
variable resistor by varying the current to the middle base
layer. As the current increases to the base lead, the transistor
passes more and more current to the collector or out lead. A
typical application for a variable resistor transistor might be
the power transistor for the blower motor in an automatic climate
A diode is a type of "one way" switch or filter that allows
current to flow in one direction only. A diode is made by
sandwiching P-type and N-type silicone crystals back to back.
The P-N junction will only flow electrons when an outside voltage
pushes the holes in the P-material towards the extra electrons in
the N-material. This happens when the applied voltage polarity
is in the same direction as the P-N junction (positive on the P
side, negative on the N side). This is called "forward bias."
When this happens, the junction conducts current.
But when current is applied in the opposite direction
("reverse bias"), the reversed polarity pulls the electrons away
from the P-N junction on the N side, and the holes away from the
junction on the P side, leaving nothing to carry the current
across the junction boundary. So the diode effectively blocks
the passage of current.
Of course, nothing is perfect and diodes are no exception.
If enough reverse bias voltage is applied, it will punch through
the diode and flow in the opposite direction destroying the diode
in the process. That why alternator diodes that convert
alternating current (AC) to direct current (DC) are usually
damaged when the battery is hooked up backwards or someone uses a
battery charger that puts out too much voltage. The voltage at
which a diode breaks down is called the "peak inverse voltage."
Exceed it and the diode is ruined.
The same precautions apply to transistors. All semiconductors are
designed to handle limited current loads, even the large power
transistors used in ignition modules and distributorless ignition
systems. If the maximum current load is exceeded, it usually
ruins the component.
"Zener" diodes are a special type of diode that are designed
to flow backwards under certain circumstances. The semiconductor
material is more heavily doped so the P-N junction will allow
reverse current flow without damage when a certain voltage level
is exceeded. These are sometimes referred to as "avalanche"
diodes because they don't pass reverse current until a certain
voltage is achieved, then they open up all at once. Zener diodes
are used in voltage regulators to provide voltage overload
Another special type of diode is the "Light Emitting Diode"
(LED). The crystal in this type of diode glows red when current
is applied much like the filament in a light bulb. But since
there's no filament to burn out, LEDs tend to be long lived.
LEDs also require less current than conventional bulbs. LEDs are
used for digital displays in some test instruments, and in some
CHMSL (center high mounted stop light) brake lights. LEDs are
also used to trigger ignition and/or injector pulses in some
engines (such as Chevrolet's Opti-Spark Ignition System or
Nissan's ECCS system).
As solid state electronics evolved, components were
miniaturized so more and more components could be crammed onto
smaller and smaller circuit boards. The "integrated circuit"
(IC) allowed a complete electronic circuit consisting of
transistors, diodes and resistors to be formed on a single
silicon wafer or "chip."
Invented by Jack Kilby of Texas Instruments in 1958, ICs are
made by plating and etching multiple layers of P-type and N-type
material over one another to form interconnecting circuits on a
tiny wafer that may be no larger than a small letter "o" on this
page! IC technology has allowed engineers to pack the electronic
equivalent of 6000 lbs. of spaghetti into a 1 lb. box!
Under a microscope, these interconnecting circuit elements
resemble a complex street map. Keep in mind, however, that it's
a three-dimensional map. The little "roads" that crisscross each
other are several layers deep with numerous underlying
interconnections like the overpasses and access ramps on an
intercity expressway. But the layers are extremely thin, only a
few microns thick at most.
These integrated circuits may be combined like building
blocks to create even larger more complicated chips. For
example, "very large scale integration" (VLSI) refers to ICs that
contains 50,000 or more such building blocks.
The silicon chip that contains the integrated circuits may be
packaged several different ways. One is to mount the chip on a
flat ceramic or metal plate so it can be installed on a printed
circuit board. This is done by soldering the IC's leads to the
Another type of packaging that's used to encapsulate the
chip with plastic. The surrounding plastic not only supports the
chip but protects it against corrosion. An example would be
Ford's Thick Film Integrated (TFI) ignition module.
Replaceable IC's that are found inside electronic control
modules (ECM's) and other electronic devices are usually square
or rectangular in shape, with anywhere from 16 to 28 pins in rows
underneath like the legs of a caterpillar. The pins allow the IC
to be plugged into a circuit board -- which eliminates the need
for soldering and allows the IC to be removed and replaced should
that be necessary. Examples of this type of IC include the
"Program Read Only Memory" (PROM) chips and Electronically
Erasable Program Read Only Memory (EEPROM) chips used in General
Motors ECMs and other automotive computers. The PROMs or EEPROMs
are used to program the engine's fuel and ignition curves as well
as other emission functions. The PROM or EEPROM chip calibrates
the engine control computer for a specific vehicle application.
This is necessary because different accessories or drivetrain
combinations can affect a vehicle's emission performance. An
engine with an automatic transmission, for example, may require a
different spark curve than a manual transmission.
PROM chips cannot be reprogrammed but they can be replaced
with a new PROM that contains different or updated instructions.
Replacing a PROM with one that contains updated information is
sometimes necessary to cure a specific driveability or emissions
problem. If a vehicle manufacturer believes a problem is due to
the computer's calibration, it may issue a Technical Service
Bulletin (TSB) describing the problem and announcing the
availability of a new or updated replacement PROM. The PROM can
then be obtained from the new car dealer and installed in the
With EEPROMS, physical replacement isn't necessary to
recalibrate a computer. An EEPROM can be reprogrammed by
downloading updated instructions through the computer's
diagnostic hookup. To prevent "unauthorized" tampering with the
EEPROM's instructions, special access codes are required -- which
are only available to new car dealers at this time.
One of the major advantages of using ICs rather than
conventional circuit boards with soldered individual circuit
components is reduced power consumption. An IC can do the same
job on a fraction of the amperage required to run a similar
large-scale circuit. But because the circuit elements in an IC
have been reduced to such tiny proportions, there's a limit as to
how much voltage and current they can safely handle. The limit
for most ICs is 20 volts or less, and current ratings are
measured in milliamps.
The reason for the power limitation is heat. The more
current an electronic circuit carries, the more heat it
generates. If the heat is concentrated in a tiny device such as
an IC, it can produce temperatures high enough to damage or
destroy the chip. That's why the IC's role in most electronic
devices is usually limited to information processing or
controlling rather than switching or handling the voltages and
currents that make things happen.
With an ignition module or a voltage regulator, the control
output from the IC is used to switch a power transistor on and
off. The power transistor can safely handle larger voltages and
currents, but the IC cannot -- which brings us to the question of
reliability. As long as an IC is operated within its voltage and
current limits, it is generally more reliable than a large-scale
electronic circuit with individual soldered components.
The main reason why most electrical and electronic circuits
fail is because of breaks in connections between circuit
components rather than the outright failure of individual
components. The overlapping circuit elements within an IC are
deposited on top of one another by a plating and etching process,
so there's little chance of anything wiggling or vibrating loose.
And if the IC is encapsulated in plastic, the circuits are
protected against environmental contamination and corrosion as
well. But that doesn't make ICs immune to trouble because the
pin connectors that link the chip to the outside world are the
Soldered pin connections can and do break loose, causing
opens that result in circuit failures. The pins on the push-in
variety of ICs can also be bent or broken during installation.
That's why GM recommends using a special tool to remove and
install PROM chips in their ECMs. The IC pins must also fit
tightly in the circuit board receptacle and be corrosion free.
ICs are most vulnerable, however, to damaging voltage spikes.
Because the overlapping circuit layers on the chip are so thin,
it doesn't take much of an overload to destroy a connection. And
once a chip is damaged, it's history.
Voltage spikes can occur when an electrical connection is
broken while a circuit is still hot. An example would be
unplugging an engine sensor or wiring connector while the
ignition is on. The sudden break in the circuit causes the
voltage to momentarily surge, creating a spike that may be as
high as 50 or 60 volts in a circuit that normally sees only 5 or
12 volts. The surge occurs because the electrons want to keep
flowing as the circuit is being broken. They pile up and try to
push their way across the gap, creating a transient voltage spike
that can fry a chip. The car makers "harden" their electronic
circuits by building in voltage overload protection, but
safeguards may not be enough to protect the chips under all
circumstances. So never disconnect or connect any wiring
connector or electronic component when the ignition is on because
some components receive current directly from the battery.
Voltage surges and spikes can also be created by arc and MIG
welding equipment. As a precaution, the battery should be
disconnected prior to welding. If welds are being made in the
close proximity of an electronic control module or other device,
the module or device should also be unplugged for additional
Potentially damaging voltage overloads can also be created by
electrostatic discharges. Sliding across a vinyl seat can build
up a static electrical charge of thousands of volts. The actual
amperage of such charges isn't much, but the voltage can be high
enough to produce a visible (and sometimes painful) shock when
you touch a conductive surface. If the thing you touch happens
to carry the voltage back to a computer chip, the spark can
literally punch a hole right through the microscopic circuit
layers of the IC leaving it permanently maimed.
When handling any type of chip based electronic module,
precautions should be used to avoid electrostatic discharges
that might damage the circuitry. You can minimize the
danger by "grounding" yourself with an anti-static wrist strap,
by placing modules and computers on non-conductive anti-static
mats, and/or by wearing cotton fiber clothing.
TESTING & DIAGNOSIS
Since there's no practical way for a technician to test or
repair faulty integrated circuit chips inside a control module,
your only option is to replace the module if it isn't working
correctly (unless, of course, it's a situation where the problem
is really module calibration and there is an updated PROM chip
for the module, or new programming for an EEPROM). But first you
have to isolate the problem to the module by following a detailed
step-by-step diagnostic procedure.
With transistors and diodes that are not part of an
integrated circuit, it is possible to replace individual circuit
components in some instances (the diodes in an alternator, for
example). But in most instances, the labor to do so is too
time-consuming so the entire unit is replaced if a circuit