First Character - System
The first character identifies identifies the system related to the trouble code.

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

Second Digit - Code Type
The second digit identifies whether the code is a generic code (same on all OBD-II equpped vehicles), or a manufacturer specific code.

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

Third Digit - Sub-System
The third digit denotes the type of sub-system that pertains to the code

1 = Emission Management (Fuel or Air)
2 = Injector Circuit (Fuel or Air)
3 = Ignition or Misfire
4 = Emission Control
5 = Vehicle Speed & Idle Control
6 = Computer & Output Circuit
7 = Transmission
8 = Transmission
9 = SAE Reserved
0 = SAE Reserved

Fourth and Fifth Digits:
These digits, along with the others, are variable, and relate to a particular problem.
For example,a P0171 code means P0171 - System Too Lean (Bank 1).
To lookup your particular code, visit our OBD Trouble Codes section.