What does it mean?
Modern vehicles have dozens of modules onboard. The transmission control module (TCM) is one such module. The TCM takes inputs from various sensors and uses that information to control transmission output devices. In a vehicle equipped with a communication area network, the TCM shares this information with other modules over a communication bus. An example of a controller area network (CAN) All modules on the bus have at least one other module they report their state of health to.
If a module fails to send a state of health message, the companion module will set a DTC for the module that did not respond. Code P0864 stands for Transmission control module (TCM) communication circuit -range/performance problem. This code indicates the TCM did not respond when addressed by its companion module.