The TSS or turbine speed sensor is mounted in the transmission and measures the rpm of the input shaft versus the speed of the output shaft. This helps the PCM determine if the transmission gears are holding as they should. This allows the PCM to adjust shift times and pressures due to normal wear on the components inside the transmission. If the readings become out of range so far the PCM cannot compensate or the data is erroneous, the computer will set a code. These codes aid in the diagnosis of the transmission/sensors.
