The P2118 OBD2 fault code setting means that the Powertrain Control Module (PCM) observed a malfunction in the throttle actuator control system.
To control the throttle actuator, the PCM constantly monitors the Throttle Position Sensor (TPS). The proper throttle body function is determined by the position of the throttle plate, which is controlled by one or more throttle actuator engines. The PCM also monitors the TPS sensor to know the speed the driver wants to go and to determine the proper throttle response. To do this, a current flow moves the throttle plate to the desired position.