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

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

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.
2. Tests for proper power inputs to the primary shift selector.
3. Tests for wiring defects between the primary shift selector and the connection to the J1939 backbone.

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