COMPUTERS - HOW THEY WORK MAKING
SENSE OUT OF ONE'S AND ZEROS...
WHAT IS AN AUTOMOTIVE COMPUTER? The computer, also known as the "brains"
or Eelectronic Control Module (ECM) is a microprocessor that converts electrical
inputs from sensors into electrical outputs. These outputs are used to
control actuators, relays, switches, and various solenoids found throughout
The computer system consists of inputs,
processing, and outputs...
When an engine is started, the computer uses information from the sensors
to regulated the air-fuel mixture: namely coolant temperature, barometric
pressure sensor, and the air temperature sensor.
- As the engine starts, information about idle speed, timing, and fuel
mixture are stored in adaptive memory to keep the engine running
while it is cold or running in 'Open Loop' mode.
- While the engine is running, it heats up quickly and the computer goes
into 'Closed Loop' mode.' In this mode, the oxygen sensors (located
in the exhaust system) sends a voltage signal to the computer, and the
computer starts adjusting fuel at the injectors, spark timing at the spark
plugs, and idle speed to control the engine.
WHAT ARE THE MAIN DIVISIONS OF AUTOMOTIVE COMPUTERS? A typical automotive computer consists
of six main divisions: reference voltage, signal amplifier, analog
to digital converter, output drivers, memory, and ECM grounds. As soon as
the engine starts, the ECM quickly goes into self-test mode to verify if
all sensors and actuators are working properly. If a fault occurs, the
ECM turns on the “check engine” light and a code is stored in memory. See
photos - Click
Here for More Information.
HOW DO YOU TEST AUTOMOTIVE COMPUTERS? Automotive computers are easy to diagnose.
If they are good - they work. If they are bad - they don't work! One of
best ways to tell if your computer is bad is to eliminate POWER and GROUND
problems. Use an electrical schematic to identify and test for good B+ or
battery positive , B- or battery negative, and key-on ignition switch
voltage. If there is no voltage on the B+ side, check for blown fuses or
damage wires and connectors.
If you suspect a poor ground circuit at
the computer, run a voltage drop test at the computer and check for ground
at the B- or battery negative terminal. Use an electrical schematic to
check for multiple ground connections and test each ground separately.
Another easy test for computers is to verify
there is communication with your scan tool. If there is no communication
at the Data Link Connector (DLC) - this is where you plug-in your scan tool
to the vehicle's computer, check for corrosion at the
computer pins, bent pins, or blown fuses. Once you have eliminated all
problems listed above, you can now suspect a bad computer.
Keep in mind that if a computer fails, there
is always a reason WHY. The quicker you find out, the happier you and your
customers will be.
HOW DOES AUTOMOTIVE COMPUTERS WORK?
Automotive computers work on the principle
of digital electronics and binary coding. In digital electronics, the computer
uses billions of transistors and semi-conductors to turn electrical circuits
ON and OFF. A computer does not understand our system of communication through
spoken or written languages. Nor does it understand our sense of sight,
sound, and touch. These human senses can be communicated electrically,
through the use of a simple computer language called binary
Binary coding uses a series of 1's (switch ON) and 0's (switch OFF) to give machines
intelligence or logic. This computer language system enables machines to do complex tasks such as
monitoring, translating, interpreting, deciding, and even manipulating
or controlling motors, relays, and other devices.
Now it's your turn! See if you can determine
how computers change our decimal numbering system into binary codes in order to energize
fuel injectors during various power needs of the engine.
If you notice in the diagram below...
1 ms injector pulse width equals a binary
code of 0001 for IDLE LOW POWER and a 10% duty cycle or narrow injector
3 ms injector pulse width equals a binary
code of 0011 for MEDIUM POWER and a 50% duty cycle or medium injector pulse
5 ms injector pulse width equals a binary
code of 0101 for WIDE OPEN THROTTLE HIGH POWER and a 90% duty cycle or
wide injector pulse width
The computer uses binary
tables stored in memory
to adjust air-fuel ratios of the engine. Binay tables can also be used to provide data for the computer to energize
a starter motor when the ignition switch is turned-on and the neutral safety
switch is in Park or Neutral positions.
Read the binary table below (interpet each row and column)...