Actron OBD II AutoScanner CP9135 Instructions Manual page 37

About Diagnostic Trouble Codes (DTCs)
Engine computers can find problems
The computer systems in today's vehicles do more than control engine
operations—they can help you find problems, too! Special testing abilities are
permanently programmed into the computer by engineers. These tests check
the components connected to the computer which are used for (typically):
fuel delivery, idle speed control, spark timing, emission systems, and
transmission shifting. Mechanics have used these tests for years. Now you
can do the same thing by using your OBD II AutoScanner!
Engine computers perform special tests
The engine computer runs the special tests, depending on the manufacturer,
engine, model year, etc. There is no "universal" test that is the same for all
vehicles. The tests examine INPUTS (electrical signals going INTO the
computer) and OUTPUTS (electrical signals coming OUT of the computer),
as well as internal calculations made by the computer. Input signals which
have "incorrect" values, or output circuits which do not operate properly are
noted by the test program and the results are stored in the computer's
memory. These tests are important. The computer cannot control the engine
properly if it has incorrect input information or faulty output circuits.
Code numbers reveal malfunctions
Malfunctions are stored by using code numbers, usually called "diagnostic
trouble codes" or "DTCs." For example, a code P0122 might mean "throttle
position sensor signal voltage is too low." Generic code meanings are a part
of your OBD II AutoScanner's software. Manufacturer specific DTCs will
require the use of a vehicle service manual. See page 2-5 for more information
on ordering service manuals or on the enclosed product CD.
Read trouble codes
To find the cause of the problem yourself, you need to perform special tests
called "diagnostics." These procedures are in the vehicle's service manual.
There are many possible causes for any problem. For example, suppose you
turned on a wall switch in your home and the ceiling light did not turn on. Is
it the bulb, light socket, wiring, or wall switch? Maybe there is no power coming
into the house! As you can see, there are many possible causes. The
diagnostics written for servicing a particular trouble code take into account
all the possibilities. If you follow these procedures, you should be able to find
the problem causing the code and fix it yourself.
Using the OBD II AutoScanner is fast and easy. Trouble codes give you
valuable knowledge - whether you go for professional service or do it yourself.
Now that you know what trouble codes are and where they come from, you
are well on your way to fixing today's computer-controlled vehicles! Once you
have read the DTCs, you can either:
• Have your vehicle professionally serviced, or
• Repair the vehicle yourself using the diagnostic trouble codes to help
locate the source of the problem.
With the OBD II AutoScanner, you can also monitor the operation of systems
in the vehicle, helping to pinpoint the system where there may be a problem.
About OBD II
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