DTC U0291 Lost Communication With Gear Shift Module (Shift Selector) 2

U0291 - Lost Communication 

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 U0304 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 U0304 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.
Read More: How to Connecting ALLISON Transmission using ALLISON DOC Software
• 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.

#Test Description of DTC Steps
This DTC requires the use of the J 47275 TCM Breakout. The numbers below refer to step numbers on the diagnostic table.
1. Tests for proper power inputs to the primary Shift Selector.
Test the following primary Shift Selector circuits for an open or short-to-ground:
The battery power supply including fuses, if applicable.
The ignition sense circuit.
The ground return circuit.
NOTE: DTC U0103 indicates the TCM did not detect a state of health message from the primary Shift Selector for 2 or more seconds. This may indicate an open in Shift Selector wiring or a defective Shift Selector. Did you find and correct the condition?

2. Tests for wiring defects between the primary Shift Selector and the connection to the J1939 backbone.
Turn ignition OFF.
Disconnect the 80-way connector at the TCM and install J 47275 TCM Breakout.
Disconnect the shift selector(s).
Inspect the CAN backbone between the TCM and Shift Selector(s) for defects.
At J 47275-1 TCM Overlay, test for wire-to-wire shorts, and shorts-to-ground, and opens between Shift Selector at pins 8 (CAN Lo1), 28 (CAN Hi1), 48 (CAN Hi2), and 68 (CAN Lo2), if used.
At J 47275-1 TCM Overlay, test for wire-to-wire shorts and opens between shift selector at pin 49
If TCM internal termination resistor is used, test for opens, wire-to-wire shorts, and shorts-toground at pin 7 (internal resistor). Were any wiring defects found?
Coordinate with the vehicle OEM to repair or replace the vehicle wiring. Is the repair complete?
Replace the primary shift selector. Is the replacement complete?

3. To verify the repair:
Install Allison DOC™ For PC–Service Tool.
Clear the DTC.
Verify the TCM responds to Shift Selector commands.
Refer to Allison DOC™ For PC–Service Tool Test Passed section and confirm the test was run.
Did the DTC return?


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