Diagnostics communication: Notes
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
Diagnostics communication is over the cable from pin 11 of the TC/ABS control module to pin 8 of the data link connector, and from there direct to the diagnostic instrument.
The diagnostic tool communicates digitally and serially with the TC/ABS system. With digital communication, the difference in voltage between the lead and ground has two values, in this case about 0 V and B+. The information is coded so that different combinations of 0 V and B+ pulses Have different meanings.
With serial communication, the information is sent in "packets" which are sent one after the other in very quick succession.