U2105

ALLISON AUTOMATIC TRANSMISSION

DTC U2105

DTC U2105 Step 1 -6:

Circuit Description for Allison Automatic Transmission
The Transmission Control Module (TCM) can be calibrated to communicate with an electronically-controlled engine via SAE J1939. Diagnostic information is also communicated via SAE J1939. This DTC applies to the 6.6 L engine only. DTC U2105 is a type B DTC.

Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9V and less than 18 V.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.

Conditions for Setting the DTC
DTC U2105 sets when the TCM detects one of the following conditions:
^ The TCM is calibrated for J1939 communication and the TCM detects an error on the CAN link, no engine throttle or torque messages, for 3 seconds.
^ An open at the CAN backbone, i.e.-missing resistor or open connection.

Action Taken When the DTC Sets
^ DTC U2105 is stored in the TCM history.
^ The MIL illuminates on the second occurrence.
^ The TCM uses the default throttle value.
^ The TCM halts shift adapts (DNA).
^ The TCM inhibits TCC engagement.

Conditions for Clearing the MIL/DTC
A scan tool can clear the code 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
^ Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation.
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a fault.
^ If this DTC is present in a new vehicle, harsh shifting may occur since shift adaptive action is inhibited.
^ In certain applications, vehicle cruise control function may be used to verify if J1939 is operating properly. If this function is not operating, the engine controller may not be broadcasting a J1939 signal. This could be due to incorrect parameter setting at the ECU or a defective ECU. The vehicle OEM should be contacted to verify proper ECU setting.
^ Intermittent cycling of the TCC could indicate that a J1939 wiring problem exists. It is possible to have an open condition in the J1939 wiring and U2105 not set or only set when an open condition at the J1939 is present over the period of time needed to allow the U2105 to set.
^ It is necessary to have two 120 Ohm resistors installed in the J1939 Controller Area Network (CAN).

Test Description
The numbers refer to the step numbers on the diagnostic table.
2. This step checks for loose CAN connectors.
4. This step checks resistance between pins 29 and 32 on the C1 connector.