Diagnostic Trouble Codes or DTCs
In the past malfunction code numbers varied between manufacturers, years, makes and models. OBD II requires that all vehicle manufacturers use a common Diagnostic Trouble Code or DTC numbering System.
There is a generic DTC listing that all manufacturers must use. Since the generic listing was not specific enough, most manufacturers came up with their own DTC listing, which are called manufacturer specific codes. Both generic
and manufacturer specific codes are 5 digits.
The first digit is a letter, which identifies the function of the device, which has the fault.
This digit can be either
P Powertrain
B Body
C Chassis
U Network or data link code
The second digit is either a 0 or 1 and indicates whether the code is generic or manufacturer specific.

0 Generic
1 Manufacturer Specific

The third digit represents the specific vehicle system that has the fault.
Listed below are the number identifiers for the powertrain system.

1 Fuel and Air Metering
2 Fuel and Air Metering (Injector Circuit Malfunctions Only)
3 Ignition System or Misfire
4 Auxiliary Emission Control
5 Vehicle Speed Control and Idle Control System
6 Computer and Auxiliary Outputs
7 Transmission
8 Transmission
The last two digits indicate the specific fault index.
On OBD II vehicles there are two different types of DTCs: Stored and Pending. For a DTC to become Stored, certain malfunction conditions must occur. The condition(s) required to Store a code are different for every DTC and vary by vehicle manufacturer. In order for some DTCs to become Stored, a malfunction condition has to happen more than once. If the malfunction conditions are required to occur more than once, the potential
malfunction is called a Pending DTC. The DTC remains Pending until the malfunction condition occurs the required number of times to make the code Stored. If the malfunction condition does not occur again after a set time the Pending DTC will be cleared.

OBD II Inspection and Maintenance (I/M) Readiness Monitors
A monitor is a piece of software in one of the vehicle's on-board computers that has the job of monitoring a specific piece of the engine. There are two types of monitors: continuous and non-continuous.
A continuous monitor runs continuously during vehicle operation. A non-continuous monitor requires enabling criteria to make it run. Some examples of enabling criteria are vehicle acceleration/deceleration to a certain speed, engine temperature and driving the vehicle at a certain speed for a period of time.

For OBD II vehicles, there is a fixed list of 11 monitors: 3 continuous and 8 non-continuous. The 11 monitors are not applicable for all vehicles. The Inspection & Maintenance screen of the software lists the availability and status of your vehicles monitors. In order to pass an emission inspection all of the supported monitors must be completed.

The Continuous Monitors are:
•Misfire •Fuel System •Components

The Non-Continuous Monitors are:
•Catalyst •Secondary Air System •Oxygen Sensor
•Heated Catalyst •A/C System •Oxygen Sensor Heater
•Evaporative System •EGR System