Allison - Automatic Transmission

DTC P0742

Circuit Description

The transmission control module (TCM) uses data from the engine speed sensor and the turbine speed sensor to calculate the torque converter slip value. The TCM then compares this calculated slip value to a preset value in the TCM calibration.


DTC P0742 is a type B DTC.


DTC Descriptor

This diagnostic procedure supports the following DTC:


DTC P0742 Torque Converter Clutch (TCC) System - Stuck On


Conditions for Running the DTC

* DTC P0122, P0123, P0716, P0717, P0721, P0722, P0743 are not active.
* The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
* Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
* The transmission must be in a forward range.
* The torque converter clutch (TCC) is not enabled or requested.



Conditions for Setting the DTC

DTC P0742 sets when the TCM detects TCC slip speed values indicating a stuck on or locked condition for 2.5 seconds.


Action Taken When the DTC Sets

* The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* If failure occurs before shifting is completed, the transmission will shift to NEUTRAL. If failure occurs while shifting is being completed, the transmission will shift to NEUTRAL or 1st range while diagnostic response is active.
* If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL.
* If the shift selector is moved to REVERSE, the transmission will shift to NEUTRAL or REVERSE.
* If the shift selector is returned to DRIVE, the transmission will shift to NEUTRAL or 1st range.
* DTC P0742 is stored in TCM history.
* The TCM inhibits TCC engagement.
* The TCM freezes shift adapts.



Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.


Diagnostic Aids

* Inspect the wiring for poor electrical connections at the TCM. Inspect 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 condition.



Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for TCC application at startup, stuck on.
3. This step inspects for internal damage.
4. This step inspects for 3 possible causes for the TCC being stuck on.