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About Diagnostic Trouble Codes (DTCs)
Where do they come from and what are they for?
Engine computers can find problems
The computer systems in todays 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 Actron OBD
II System Tester!
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 computers 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 test results
The test results 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 System
Testers softwareall you have to do is look them up! Manufacturer specific DTCs will
require the use of a vehicle service manual. See page 2 for more information on
ordering service manuals.
Read Trouble Codes with the OBD II System Tester
You can obtain DTCs from the engine computer by using the OBD II System Tester.
You can also monitor the operation of systems throughout the vehicle, helping to
pinpoint the system where there may be a problem. 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.
Diagnostic Trouble Codes and Diagnostics help you fix the problem
To find the cause of the problem yourself, you need to perform special test proce-
dures called diagnostics. These procedures are in the vehicles 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 a bad bulb or
light socket? Are there problems with the wiring or wall switch? Maybe there is no
power coming into the house! As you can see, there are many possible causes. The
diagnostics are 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.