Rotational speed sensor for output shaft, signal interference
Check that there is no damage or short circuit on the external cable harness. Contact an Allison dealer.
What you'll see
No driver-visible symptom recorded.
System reaction
The Allison fault code number is: P0721.The fault code can only be set when the following is fulfilled: Output shaft speed is greater than 200 rpm.Gear shift must be completed and current gear not be neutral.If the fault occurs when driving with the selected forward gear and a gear shift has been carried out, the gearbox maintains the current gear.If the fault occurs when driving with selected forwards gear range and gear shift is in progress, the gearbox returns to the previous gear after which the gearbox carries out the requested gear shift.The lock-up cannot be locked.The fault code is cleared automatically, when the vehicle has completed 40 start-up cycles without the fault being detected again.
Diagnostic depth
The control unit has detected a disturbance in the signal from the rotational speed sensor which is located on the output shaft.
A possible cause of the fault may be damage to the cable harness or a defective rotational speed sensor for the output shaft.