Circuit/System Description
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control module (TCM) sends vehicle speed data to the engine control module (ECM). The data is sent to the ECM through a high speed network called the GM control area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P0864 to set by itself. If a CAN fault occurs, other DTCs set before DTC P0864.