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4
GENERAL INFORMATION
On-Board-Diagnostics (OBD) II
The OBD II system is designed to monitor emission control systems and
key engine components by performing either continuous or periodic tests
of specific components and vehicle conditions. When a problem is
detected, the OBD II system turns on a warning lamp (MIL) on the vehicle
instrument panel to alert the driver typically by the phrase of “Check
Engine” or “Service Engine Soon”. The system will also store important
information about the detected malfunction so that a technician can
accurately find and fix the problem. Here below follow three pieces of
such valuable information:
•
Whether the Malfunction Indicator Light (MIL) is commanded ‘on’ or ‘off’;
• Which, if any, Diagnostic Trouble Codes (DTCs) are stored;
• Readiness Monitor Status.
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 the
control system which 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 set. On the next page is an
example to illustrate the structure of the digits.
Location of the Data Link Connector (DLC)
The DLC (Data Link Connector or Diagnostic Link Connector) is the standardized
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. For
some Asian and European vehicles, the DLC is located behind the ashtray and
the ashtray must be removed to access the connector. Refer to the vehicle’s
service manual for the location if the DLC cannot be found.
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