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DTC U0404 Invalid Data Received From Gear Shift Module (Shift Selector) 1

DTC U0404 Invalid Data Received From Gear Shift Module (Shift Selector) 1




Circuit Description
In Allison 4/5th Generation Controls, the Transmission Control Module (TCM) communicates with the shift selector over the J1939 Controller Area Network (CAN). Allison J1939 shift selectors broadcast proprietary messages to the TCM related to range selection and other operating modes.

Conditions for Running the DTC
• Battery voltage is greater than 9 volts
• Engine speed is within a calibration range

Conditions for Setting the DTC
The TCM sets DTC U0404 when the primary shift selector does not receive valid data identifying the selector. OEM shift selectors must be approved for use.

Action Taken When the DTC Sets
• The CHECK TRANS light is illuminated
• Lock in neutral. Unable to select range.
• DTC U0404 is stored in the TCM history

Conditions for Clearing the DTC/CHECK TRANS Light
• DTC may go inactive by restarting the engine if the selector was not recognized due to battery voltage issues.
• Use the Allison DOC™ For PC–Service Tool to clear the code from the TCM history.
• The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 engine starts without a reoccurrence of the code.

Diagnostic Aids
• DTC occurs if a prognostic-capable calibration is used with a non-prognostic shift selector.
• Typical causes for this DTC include:
-OEM selector and/or TCM power and ground wiring issues
-Low vehicle batteries
-Master disconnect switch issues
-Low cranking voltages
-OEM J1939 wiring issues, such as data link wiring shorted to ground, data link wiring open circuited, data link shielding problems, data link termination resistors missing, defective, or unplugged
• If there are other vehicle DTCs present, the cause for transmission-related DTCs might be external to the transmission and those vehicle systems must be corrected in order for the transmission DTCs to be resolved.
• A transmission DTC must be active during the troubleshooting process to determine what caused the DTC. Use the Snapshot feature and/or Databus Viewer of Allison DOC™ For PC–Service Tool while operating the vehicle in the same conditions listed in the Failure Record (available in the Allison DOC™ For PC–Service Tool Reports menu).
• Using the Snapshot feature and/or Databus Viewer of Allison DOC™ For PC–Service Tool and/or a DVOM and the Breakout Box J 39700 while manipulating the chassis harness and/or data link wiring may reveal intermittent shorts to ground, shorts to another circuit, and open circuits that are causing an intermittent DTC.
• OEM chassis wiring issues should be considered as possible causes for every DTC. Possible wiring and connector issues include:
-J1939 termination resistors may be disconnected or defective

-Expanded female terminals in a connector. Use a mating pin or terminal to check for a light drag feel when the mating terminal or pin is inserted and slowly removed. There should be some slight friction between the matching terminal and pin combination. Expanded terminals have no feel of drag when the matching pin or terminal is inserted and removed.

-Broken terminal locks allow the pins or terminals to push back into the connector resulting in poor connection or pin to pin shorts in the connector. Inspect for broken locks and displaced terminals in connections. Never use paper clips or other devices to back-probe a connector while doing Allison service work.

-Poor pin crimps. Pin crimps should be pull-tested by the technician to verify the crimp is secure to the wire. If the pin crimp is loose, the pin easily moves or even comes off the wire with a slight tug on the terminal by the technician. This situation may not reveal itself as an active DTC but instead may exhibit other symptoms like shift quality issues.

-Connector and pin corrosion caused by moisture in connectors. Empty wire locations in connectors must always have a plug to keep moisture from finding a path into the connector.

-Poor harness routing and improper strain relief may cause damage resulting in electrical open and/or short circuits to wires and connector components.

-Butt splices and wire ties are not an ideal solution for any transmission repair. If butt splices will be used, then always use heat-shrinkable butt splices. Never use wire ties inside the transmission, to hold connector components together in the place of a connector lock, or in the place of the correct strain relief components and clips used to fasten harnesses to the vehicle or to retain vehicle connectors unless OEM approved for the location and vehicle component being repaired.

• The following procedures are not documented in any Allison service procedures or in any Allison Troubleshooting Manual or Service Manual and therefore should not be used as a method to diagnose any transmission DTC(s), function, or shift quality concern:
-Back probing any connectors used for transmission features or functions may damage and/or unlock the terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J 39700 Breakout Box, appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

-Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use Breakout Box J 39700 and appropriate harnesses with Allison DOC™ For PC–Service Tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting Manuals to use a digital volt-ohm meter (DVOM) with the Breakout.

-Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

Test Description of DTC Steps
1. Review of general troubleshooting procedures and DTC service tips.
2. Check DTC active.
3. Check for approved selector.
4. Check vehicle wiring.
5. Confirm repair is successful.


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