Allison Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0742





Circuit Description for Allison Automatic Transmission
The Transmission Control Module (TCM) uses data from the engine speed sensor and the input 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.

Conditions for Running the DTC
^ DTC P0122 and DTC P0123 are not active.
^ DTC P0716 and DTC P0717 are not active.
^ DTC P0721 and DTC P0722 are not active.
^ DTC P0743 or P1860 is not active.
^ The components are powered and ignition voltage is greater than 9 V and less than 18 V.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
^ The throttle position is in the 10-90 percent range.
^ Must be in forward range.
^ The torque converter clutch 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

Action Taken When the DTC Sets
^ If failure occurs before shifting is completed, then the transmission will shift to NEUTRAL. If failure occurs while the shifting is being completed, then the transmission will shift to NEUTRAL or 1st range while diagnostic response is active.
^ If the shift selector is moved to NEUTRAL, then the transmission will shift to NEUTRAL.
^ If the shift selector is moved to REVERSE, then the transmission will shift to NEUTRAL or REVERSE.
^ If the shift selector is returned to DRIVE, then the transmission will shift to NEUTRAL or 1st range.
^ DTC P0742 will be stored in the TCM history.
^ The TCM inhibits TCC engagement.
^ The TCM freezes shift adapts (DNA).
^ Illuminates the MIL when active.
^ 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.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for TCC application at start-up (stuck on).
3. This step checks for internal damage.
4. This step checks for three possible causes for TCC being stuck on.