|Trouble Code||Fault Location||Probable Cause|
|U0404||Invalid data received - gear shift module|
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What Does Code U0404 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.
What are the common causes of code U0404?
- A defective system power relay
- Corroded or damaged fuses or fusible links
- Loose, corroded, or disconnected ground wires and/or straps
- Cut, burnt, or otherwise damaged wiring harnesses or connectors
- A defective gearshift module
- A defective PCM or transmission controller
What are the symptoms of code U0404?
- Reduced transmission performance
- Diminished engine fuel efficiency and performance
- Erratic transmission shifting patterns
- Illumination of the service engine soon lamp, traction control lamp, or antilock malfunction lamp
- Inoperative speedometer
- Inoperative paddle shifter/s
- Inoperative mode selector switch
How do you troubleshoot code U0404?
I would begin my diagnosis of a U0404 Invalid Data Received from Gear Shift Control Module code with a careful (albeit practical) visual inspection of all system wiring and connectors. I always include an inspection of the battery, battery cables, and battery terminal ends in my diagnosis. Clean, repair, or replace damaged, burnt, or corroded wiring and/or components as required. Test all system fuses, circuit breakers, and power supply relays and replace defective parts as necessary.
One might proceed by retrieving and making a notation of all stored trouble codes and available freeze-frame data before clearing the codes and continuing with their diagnosis.
Some type of diagnostic scanner, a digital volt/ohmmeter (DVOM), and a manufacturer’s service manual will prove instrumental in a correct diagnosis of this code.
The most straightforward method for determining whether the gearshift module is providing an input signal to the PCM is via a scanner (if available). After the scanner has been placed in such a mode as to view the system data stream, observe the perceived position of the gearshift as it is moved through its range of movement. Note the perceived input signal position of the gearshift as it corresponds to the actual position and make note.
If the actual gearshift position fails to correspond with the perceived position, continue by verifying that all mechanical aspects of the gearshift mechanism (don’t overlook the shifter cable) are operating properly. Repair loose, worn, binding, or broken parts as required.
Should the mechanical aspects of the gearshift mechanism prove to be intact, continue by testing the output signal of the gearshift control module using the scanner and the DVOM. Consult the service manual to determine what the appropriate signal must be from the gearshift control module.
If the gearshift control module fails to provide an acceptable output signal, continue by testing for system power and ground signals. If either of these signals prove to be absent, check the service manual to discover their respective points of origin and resume your testing at the designated point. Power to this type of module is generally supplied using some type of relay. System ground signals are most likely furnished via a chassis ground or central engine ground. Consult the manufacturer‘s service manual for the exact location of each system grounds.
Should the system ground and voltage signals prove to be present, and gearshift control module output signals are not, suspect an internal malfunction in the gearshift control module.
If the gearshift control module provides an output signal that is not received by the PCM, disconnect all electrical connectors from related controllers and use the DVOM to test resistance and continuity on each individual system circuit. Be careful to remove electrical connectors from controllers before testing resistance and continuity (using the DVOM) on system circuits. Failure to do so may result in controller damage. Repair or replace open or shorted circuits as required. System circuits may be shorted to ground or voltage. They may also be open.
Depending upon the location of the faulty circuit, it may prove advantageous to replace it as opposed to repairing it. Circuits that are “buried” deep in a bulky harness, circuits that are hidden in and under the dash, and circuits that pass through a bulkhead are virtually impossible to physically locate and repair. These types of circuits are more easily cut and replaced using a section of wiring of an identical gauge and similar length. I prefer to solder replacement circuits into place to provide a durable and reliable solution to the malfunction.
Now, having tested all system circuits and finding them in order, suspect an internal fault with the PCM. There is no method for testing either of the controllers mentioned herein and condemnation of these types of components is typically narrowed down to a process of elimination. Replacement of said controllers will likely require specialized reprogramming of some sort.
Codes Related to U0404
- Vehicle speed and speedometer/odometer codes
- Input and/or output speed sensor codes
- Traction control system codes
- Antilock brake system codes