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2.2 Diagnostic Trouble Codes (DTCs)
OBDII Diagnostic Trouble Codes 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.
OBDII 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 set.
Here below is an example to illustrate the structure of the digits:
DTC Example
P
0
2
0
1
B= Body
Code type
Sub Systems
C=Chassis
Gerneric (SAE)
1=Fuel / Air Metering
P=Powertrain P0, P2, P34, P39
2=Fuel / Air Metering
U=Network
B0, B3,
3= Ignition System or Engine Misfire
Identifies what
section of the
systems is
malfunctioning
C0, C3
4= Auxiliary Emission Controls
U0. U3
5= Vehicle Speed Control and Idle Controls
Manufac. Spec.
6= Computer Output Circuits
P1, P30, P33
7= Transmission Controls
B1, B2
8= Transmission Controls
C1,
C2
U1,
U2
2.3 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 can not be found.
2.4 OBD II Readiness Monitors
An important part of a vehicle's OBDII system is the Readiness monitors, which are indicators used to
find out if all of the emissions components have been evaluated by the OBD II system.
They are running periodic tests on specific systems and components to ensure that they are
performing within allowable limits.
Currently, there are eleven OBD II Readiness Monitors (or I/M Monitors) defined by the U.S.
Environmental Protection Agency (EPA).
Not all monitors are supported by all vehicles and the exact number of monitors in any vehicle
depends on the motor vehicle manufacturer's emissions control strategy.