There is three protocol for the physical interface of ODB II connector. Volvo is using the ISO 9141 interface. I think that most of them are a serial interface operating at 10.4 Kbps. There is some chip available that implement these interface from SGS-Thomson, Philips, Harris and Motorola. The chip L9637 from SGS-Thomson implement the interface ISO 9141 used by Volvo. You can get the data sheet from SGS-Thomson WEB site.

If you want to built your own tool that will reset the service reminder light, good luck. In the OBD specification there is PID (message) that have been standardized. You can get a list from SAE. There is also other code that are manufacturer specific. The message to reset the service reminder light is one of them.

At this time there is only two way to reset the light. One is the Volvo scan tool ($4000 ?) or the IPD reset tool ($300). If you had a scan tool that is ISO 9141 compatible and you did know what is the message needed to turn off the light, you could. I try to get this info from Volvo (Sweden and NA) and from the manufacturer of the IPD reset tool. I was not sucessfull. This info is only available to the manufacturer of the IPD reset tool (It is an US company that I forgot the name).

Another way to get this info is to buy the $300 tool, connect it to the car and monitor the link with a logic analyzer. Once the message in intercepted, one can probably built a reset tool for $5 of parts. BTW, the message to reset the service reminder light has changed from the 850 series to the 70 series.

If you want to find more info, take a look at the following links:

http://www.mecel.se/my_html/ssf.htm

http://www.obdii.com/obdii.html

http://www2.ari.net/avt-inc/

http://arbis.arb.ca.gov/msprog/obdprog/obdiireg.txt

http://www.carcomp.com/index.html

http://www.sae.org/

http://www.baumtools.com/

Leo Montreuil