Originally posted by GeoPappas:
If I'm not mistaken, I believe that I saw two separate OBD-I readers at Walmart for about $20-30 each the other day. They had one for Ford/Lincoln/Mercury models and one for GM models.
  Just in case anyone's missed the obvious, these
will not work with a 1996 or newer vehicle. I guess OBDâ??I didn't specify the method of retrieving error codes, and each manufacturer was left to devise it's own method by which this could be done. The $20â??$30 gadget which is here mentioned is really just a slightly fancier way of doing what can be done with an analog voltmeter and some clip leads. See <
http://dalidesign.com/hbook/eectest.html>.
  OBDâ??II, used on all 1996 and newer vehicles, specifies a more complex manner of retrieving error codes and other data, and which requires equipment that is considerably more complex and considerably more expen$ive than the $20â??$30 gadgets.
  If you have an IBM-compatible portable computer, running Windoze 3.1 or later, have a look at <
http://www.obd-2.com/>.