For OBD1 code systems, this website gives you:
Where to find the Diagnostic Connectors
Photos of the Diagnostic Connector locations
How to put the vehicle into Diagnostic Mode
How to Read the codes (includes timing diagrams)
Ability to enter your code number(s) into their database & get their meaning
How to Erase the codes from the vehicle computer memory
For OBD2 / EOBD code systems, this website gives you:
Where to find the Diagnostic Connectors
Photos of the Diagnostic Connector locations
Entering your code number(s) to get the code meaning from their database
http://codes.rennacs.com