Allison WTEC II Fault Code: 25 PID: SPN: 77 FMI: Output speed sensor, detected at 0 output rpm, Reverse range

Main code 25 occurs if the output speed sensor reports a zero speed reading while both engine and turbine speeds are approximately equal, turbine speed is above a calibration value, and neutral is not selected or commanded.

Possible Causes:
1. Output speed sensor has failed
2. The required oncoming cluth or cluthes did not come on.