To get you started: http://volvospeed.com/vs_forum/topic/47502-dtc-information/

Ignore the top paragraph that has someone "make' their own code reader. The important part is the complete list of codes.

Remember 1-1-1 is good.

Resetting codes requires you to read all of the codes for a pin setting until you have read the first code again. Then push the button for 5-7 seconds, and when the light comes on, push the button for another 5-7 seconds. Any codes that are still present couldn't be reset as the error condition has not been fixed.

There are several online sites that explain how to read codes including the 700/900 FAQs in the Brickboard (Only the "A" box):

http://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

Use a pencil and paper to write down the codes. Get the current odometer reading stored in the instrument cluster, just for fun or if the odo gear was broken.