Circuit Description
WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 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 communication network called the GM local area network (LAN). Two circuits are used to communicate LAN data between the ECM and TCM. A fault in the LAN will not cause DTC P0864 to set by itself. If a LAN fault occurs, other DTCs set before DTC P0864.
If the ECM receives invalid vehicle speed data from the TCM, DTC P0864 sets.