Patent ID: 7072748

Claim:
A method for diagnosing a failure of an output shaft speed sensor of an automatic transmission, comprising: determining whether the transmission is in a forward gear; determining whether a failure criterion exists based on at least one of a current gear, an input shaft speed, an output shaft speed, or an engine speed, if the transmission is in a forward gear; and maintaining the current gear if a downshift criterion exists, or upshifting a gear if an upshift criterion exists, if the failure criterion exists, wherein if the determined forward gear is first gear or second gear, the failure criterion comprises at least one of: (1) a lapse of a predetermined period after shifting from neutral to drive and a turbine shaft speed greater than a turbine shaft speed threshold and no signal from the output shaft speed sensor; and (2) a lapse of a predetermined period after shifting from neutral to drive and an engine speed greater than a engine speed threshold and a normal engine speed sensor signal and no signal from the output shaft speed sensor.