The TCM (Transmission Control Module) is responsible for controlling the operation of sensors and actuators, such as the Motor Speed (RPM), TPS (Throttle Position Sensor) among others signals.
The Transmission Control Module uses the information from these sensors and activates the solenoid valves, which are related to the components of the automatic transmission, such as clutches, pressure regulator and brakes.
When the Transmission Control Module detects a malfunction with one of these sensors, it sends a signal to the ECM (Engine Control Module) and this in turn activates the Service Engine Soon light. The Engine Control Module stores this diagnostic code P0700 OBDII and implies that the TCM has found a fault with the transmission controls.