OBD II Diagnostic Trouble Codes

In the past malfunction code numbers varied between manufacturers, years, makes and models. OBD II requires that all vehicle manufacturers use a common Diagnostic Trouble Code or DTC numbering System. There is a generic DTC listing that all manufacturers must use. Since the generic listing was not specific enough, most manufacturers came up with their own DTC listing which are called manufacturer specific codes. Both generic and manufacturer specific codes are 5 digits.

A description for each of the 5 digits of the OBD II DTC structure follows.

The first digit is a letter which identifies the function of the device which has the fault. This digit can be either

P Powertrain
B Body
C Chassis
U Network or data link code

The second digit is either a 0 or 1 and indicates whether the code is generic or manufacturer specific.
0 Generic
1 Manufacturer Specific

The third digit represents the specific vehicle system that has the fault. Listed below are the number identifiers for the powertrain system.

1 Fuel and Air Metering
2 Fuel and Air Metering (Injector Circuit Malfunctions Only)

3 Ignition System or Misfire
4 Auxiliary Emission Control
5 Vehicle Speed Control and Idle Control System
6 Computer and Auxiliary Outputs
7 Transmission
8 Transmission

The last two digits indicate the specific fault index.

On OBD II vehicles there are two different types of DTCs: Stored and Pending. For a DTC to become Stored, certain malfunction conditions must occur. The condition(s) required to Store a code are different for every DTC and vary by vehicle manufacturer. In order for some DTCs to become Stored, a malfunction condition has to happen more than once. If the malfunction conditions are required to occur more than once, the potential malfunction is called a Pending DTC. The DTC remains Pending until the malfunction condition occurs the required number of times to make the code Stored. If the malfunction condition does not occur again after a set time the Pending DTC will be cleared.



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