What does it mean?
If a diagnostic trouble code U0404 is exhibited, it means that the powertrain control module (PCM), transmission control module (TCM), or body control module (BCM) have detected an invalid signal from the gearshift control module. The gearshift control module is responsible for monitoring the actual position of the gearshift and providing the various controllers with the appropriate input signal to reflect actual shifter position.
In most application, the gearshift module is a housing that contains the electronic components and the mechanical parts of the gear shifter. Other systems use a gearshift sensor and a remotely located gearshift module. The PCM uses gearshift position data when calculating fuel delivery strategy, ignition timing, and certain transmission shift control functions.
If the PCM (or transmission control module) detect a vehicle speed sensor (VSS) signal that is not appropriate for the gear position input signal, a code will be stored and a service engine soon lamp may be illuminated. In addition to input data from the VSS, other input signals including (but not limited to) turbine speed sensor data, output speed sensor data, and engine RPM data are also calculated by the PCM when determining the appropriate gear designation for the actual circumstance.
This data is also used to map engine drivability and engine performance strategy. In this instance, and in the case of most vehicles that are equipped with electronic paddle shifters, overdrive select switches, and electronic mode select functions, the vehicle which exhibits a U0404 Invalid Data Received from Gear Shift Control Module code is equipped with a gearshift control module as opposed to a gearshift selector (or neutral safety/gearshift position) switch.
This type of gearshift control module is also frequently used where the vehicle is equipped with electronic traction control.