Explanation of OBD2 Codes

OBD-II codes consist of several parts. Here is an example of an OBD2 code:

P0131

Here is an explanation of what each digit in the code means:
First character – System

The first character identifies the system related to the fault code.

     P = Powertrain
     B = Body
     C = Chassis
     U = Undefined

 

Second digit – Code type

The second digit identifies whether the code is a generic code (the same on all OBD-II equipped vehicles) or a manufacturer-specific code.

     0 = Generic (this is the digit zero – not the letter “O”)
     1 = Enhanced (manufacturer-specific)

Third digit – Subsystem

The third digit indicates the type of subsystem related to the code

     1 = Emissions management (fuel or air)
     2 = Injector circuit (fuel or air)
     3 = Ignition or misfire
     4 = Emissions control
     5 = Vehicle speed and idle control
     6 = Computer and output circuit
     7 = Transmission
     8 = Transmission
     9 = SAE reserved
     0 = SAE reserved