Patent ID: 7058497

Claim:
An apparatus for determining a failure in an automatic transmission in a vehicle while running, comprising: a first detecting portion which detects an input speed of the automatic transmission; an estimating portion which estimates an input speed of the automatic transmission when the automatic transmission is in a neutral state in which transmission of power is interrupted, based on torque input from a power source of the vehicle to the automatic transmission; and a failure determining portion which determines, whether the failure in the automatic transmission is a first failure related to the neutral state of the automatic transmission or a second failure that is different from the first failure, based on the detected input speed and the estimated input speed, wherein the failure determining portion determines that the first failure related to the automatic transmission being in the neutral state has occurred when a difference between the detected input speed and the estimated input speed falls below a preset value, and determines that the second failure related to slipping of a frictional engaging element with which a gear speed of the automatic transmission is established has occurred when the difference between the detected input speed and the estimated input speed exceeds the preset value.