How to Understand OBD-II Codes and Language

On Board Diagnostics (OBD) is a term that refers to the diagnostic and reporting capability of a vehicle. The first OBD protocol was largely unsuccessful, but OBD-II has much greater capability and standardization. The following steps will show how to understand OBD-II codes and languages.

1.Recognize an OBD-II Diagnostic Trouble Code (DTC) as a 5-character code. The first character is a letter and the other four are numbers.
2.Interpret the first character as the control system that set the code. The following letters are assigned: B for Body, C for Chassis, P for Powertrain and U for Undefined. Undefined codes are not used.
3.Examine the second character to determine the code type. The digits 0, 1, 2 and 3 are used with 0 being a generic OBD-II code and 1 being an enhanced OBD-II code. The meaning of a 2 or 3 varies by system and is reserved for future use in powertrain codes. A 2 is reserved for Original Equipment Manufacturer use and a 3 is reserved for Society of Automotive Engineer use in body and chassis codes.
4.Use any digit from 0 to 9 for the third character of a DTC. This character indicates the system or subsystem where the fault occurred and its meaning varies according to the control system that set the code.

5.Study the fourth and fifth characters of a DTC. These indicate the operating conditions that caused the code and are specific to the control system. The lowest number are general malfunctions with higher numbers providing more specific information.

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