On many Allison transmissions with a push-button shift selector, stored diagnostic codes can be cleared from the selector itself.
Park the vehicle safely, apply the parking brake, and place the transmission in Neutral (N).
Turn the ignition on. The engine may remain off.
Enter diagnostic mode. On many Allison selectors, press the UP and DOWN arrow buttons at the same time until diagnostic information appears.
Review the stored codes before clearing them. This is useful because the codes help identify the original fault.
While in diagnostic mode, press and hold the MODE button for about 10 seconds. On compatible selectors, this clears the stored diagnostic codes.
Exit diagnostic mode by pressing N (Neutral) or, depending on the selector, pressing the UP and DOWN arrows together.
Cycle the ignition off and back on, then operate the vehicle and check whether the codes return.
Clearing a code does not repair the underlying problem. If the transmission detects the fault again, the code will return. Allison states that the correct diagnostic procedure depends on the transmission product family and recommends using the corresponding troubleshooting manual or Allison DOC diagnostic software.
For Allison 1000/2000, 3000/4000, or a specific code such as P0700, P0731, or P0880, the exact clearing procedure can differ by vehicle and selector type.