http://www.scangauge.com/

This won't work with the old diesels but maybe with the newer ones. It is mostly for gassers since 1996.

Any experience with ScanGuageII? It sells for $169 and looks like you get a lot for your money. It doesn't work with 2001-2003 Mercedes for some reason but it seems to work with most other vehicles since 1996 when OBDII became the standard. It works with some 1994-1995 vehicles also. There are lists on their website to show compatibilities and incompatibilities.

This is not a replacement for professional level scanners. I didn't see any mention of codes for transmissions, ABS, climate control, etc.

You can download the manual from their website in PDF form.