What I need to know about ON-Board Diagnostic Trouble Codes

The list below contains standard diagnostic trouble codes (DTC’s) that are used by some manufacturers to identify vehicle problems. The codes provide below are generic codes that may not apply to all vehicles. Vehicle manufacturers may use manufacturer specific DTC codes that are different from the codes shown below. 

Foreign vehicles may also use DTC codes different from the generic DTC codes. The Division recommends that motorists not depend on the DTC codes in this list for vehicle repairs until they confirm the generic DTC codes apply to their vehicles. The list below is for information purposes only and is not intended for use in vehicle repairs.

http://www.dmv.de.gov/services/Vehicle_Services/dtc_list.pdf

A DTC is made up of 5 digits. Knowing the composition of the code makes it is easier to trouble shoot a DTC without knowing the description of the code.

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 equipped 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.
Composition of a DTC

Diagram of a DTC

Types of DTC’s

There are two categories of DTC’s that apply to OBDII. They are listed below with Type A being the more severe.

Type A

Emissions related.
Requests illumination of the MIL after one failed driving cycle.
Stores a freeze frame DTC after one failed driving cycle.

Type B

Emissions related.
Sets a Pending Trouble Code after one failed driving cycle.
Clears a Pending Trouble Code after one successful driving cycle.
Turns on the MIL after two consecutive failed driving cycles.
Stores a freeze frame after two consecutive failed driving cycles