DTC U0103 Lost Communication With Gear Shift Module (Shift Selector) 1

U0103 - Lost Communication

Circuit Description
Allison 4/5th Generation Controls shift selectors communicate with the transmission control module (TCM) by exchanging standardized digital messages over the SAE J1939 Controller Area Network (CAN). The physical network consists of a two-wire twisted pair, two 120 Ohm termination resistors and, in most cases, a third shield wire. A 120 Ohm termination resistor is located at each end of the network to maintain good J1939 signal quality. Vehicle OEMs may chose to configure the network to take advantage of 120 Ohm resistors built in to Allison 4/5th Generation Controls TCMs and shift selectors.

Conditions for Running the DTC
Ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 9V and less than 32V (24V TCM).

Conditions for Setting the DTC
DTC U0103 sets when the TCM has not received a state of health (SOH) message from the primary shift selector for 2 or more seconds.

Actions Taken When the DTC Sets
When DTC U0103 active, the following conditions will occur:
• The CHECK TRANS light illuminates.
• DTC is stored in TCM history.
• The active shift selector will freeze the displays for 1.5 seconds, go blank for 10.5 seconds, then display cateyes, i.e. -\-, -\-.
• Direction change shifts, i.e., forward to Reverse, etc., are allowed based on PWM signal from Allison shift selectors.

Conditions for Clearing the DTC/CHECK TRANS Light
Use the Allison DOC™ For PC–Service Tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
• DTC occurs if a prognostic-capable calibration is used with a non-prognostic shift selector.
• Vehicle manufacturers can configure the controller area network to use a built-in termination resistor in Allison shift selectors by installing a jumper between pins 7 and 18 at the primary shift selector connector. OEMs are required to clearly indicate where internal termination resistors have been used.
• DTC U0103 can be caused by the following conditions:
Intermittent open between the shift selector and the connector node.
Poor connection at the shift selector or the connector node.
Intermittent open in the connector node.
Open power or ground circuit to the shift selector.
Defective shift selector.
• Inspect the J1939 CAN wires for poor electrical connections at the primary shift selector. Look for the following conditions:
Bent terminal
Backed-out terminal
Damaged terminal
Poor terminal tension
Chafed wire
Broken wire inside the insulation

#Test Description
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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