The General Motors Entertainment and Comfort serial bus

Stuart Schmitt, 1 May 2016 (prior versions 22 April 2016 & 15 February 2009)


The purpose of this web site is to present information about the General Motors entertainment and serial (E&C) bus. The E&C bus was used in certain 1987 to 2005 GM vehicles to allow for data transmission between the radio, CD changer, remote cassette player, OnStar module, and HVAC system. The E&C bus is circuit 835 in GM’s wiring diagrams, and it is carried on a dark green wire. It is wired in a star topology from a centrally located splice point. The circuit is accessible at the diagnostic connector; on OBD-II cars, it is pin 14.



Most of the what is presented on this page was determined with an oscilloscope, a homebrew microcontroller interface, and lots of trial and error. Some useful pointers came from the following sources: