The OBD is the Onboard Diagnostic Computer that monitors the CEC's, (computerized emission controls) of which your vehicle has many, such as the AFS, cat, evap,O2 etc,etc

If any of these have operated outside of the parameters set in the computer that would cause the vehicle to exceed 1 1/2 times the federal emissions standards it sets a hard code,ie. MIL light, if they operate outside of the range for a brief time, it stores a soft code.

However, the intent and purpose of the OBD computer is to eliminate guesswork as to why a vehicle has running problems.

All the advice given in the above posts, if indeed any of them are the problem, would be stored in the computer and would generate a code that is retrievable witha scan tool. This tells a person for instance, if the O2 sensor is malfunctioning, even for a brief period.

The DLC, ( diagnostic connector link) I believe is located on the right rear side of the firewall inside the engine compartment, it is a plastic narrow rectangular fiting about 2 inches long and 1/2 in. thick with 16 pins in it.

But, a special scan tool is needed to connect and read the codes. Some auto supply stores ( autozone) will scan the OBD for a small fee. A good web site is www.obdii.com for explanations and advice.

Good luck