Allison WTEC II Fault Code: 25 PID: SPN: 66 FMI: Output speed sensor, detected at 0 output rpm, 6th

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 clutch or clutches did not come on.

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