OBD-II codes consist of a number of parts. Here is a sample OBD2 code: P0171
Here is a breakdown of what each digit of the code means:
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
Here is a website that lists a large amount of generic DTC Codes:
http://www.skpang.co.uk/dtc_list.htm