Circuit Description
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
The engine control module (ECM) sends throttle position data to the transmission control module (TCM). The TCM uses this data to modify shift speeds. The data is sent to the TCM through a communication network called the controller 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 P1791 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1791.
When the TCM receives invalid throttle position data from the ECM, then DTC P1791 will set. DTC P1791 is a type A DTC.