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2.2 Diagnostic Trouble Codes (DTCs)
OBD II Diagnostic Trouble Codes are codes that are stored by the on-board
computer diagnostic system in response to a problem found in the vehicle.
These codes identify a particular problem area and are intended to provide you
with a guide as to where a fault might be occurring within a vehicle. OBD II
Diagnostic Trouble Codes consist of a five-digit alphanumeric code. The first
character, a letter, identifies which control system sets the code. The other four
characters, all numbers, provide additional information on where the DTC
originated and the operating conditions that caused it to be set. Below is an
example to illustrate the structure of the digits:
Figure 1-2: Explanation of a diagnostic trouble code.
2.3 Location of the Data Link Connector (DLC)
The DLC (Data Link Connector or Diagnostic Link Connector) is the standard-
ized 16-cavity connector where diagnostic scan tools interface with the vehicle's
on-board computer. The DLC is usually located 12 inches from the center of the
instrument panel (dash), under or around the driver's side for most vehicles. If
the Data Link Connector is not located under the dashboard, a label should be
there revealing its location. For some Asian and European vehicles, the DLC is
located behind the ashtray and the ashtray must be removed to access the
connector. If the DLC cannot be found, refer to the vehicle's service manual for
the location.
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Figure 1-3: The DLC connector (left) can be found in the area of the car interior
seen at right (black arrow).
2.4 OBD II Definitions
Powertrain Control Module (PCM) -the OBD II terminology for the on-board
computer that controls the engine and the drive train.
Malfunction Indicator Light (MIL) -Malfunction Indicator Light (Service Engine
Soon, Check Engine) is a term used for the light on the instrument panel. It is to
alert the driver and/or the repair technician that there is a problem with one or
more of vehicle’s systems and may cause emissions to exceed federal
standards. If the MIL illuminates with a steady light, it indicates that a problem
has been detected and the vehicle should be serviced as soon as possible.
Under certain conditions, the dashboard light will blink or flash. This indicates a
severe problem and flashing is intended to discourage vehicle operation. The
vehicle on board diagnostic system can not turn the MIL off until necessary
repairs are completed or the condition no longer exists.
DTC -Diagnostic Trouble Codes (DTC) these identify which section of the
emission control system has malfunctioned.
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