FAILURE DETERMINING DEVICE OF OIL TEMPERATURE SENSOR

PROBLEM TO BE SOLVED: To determine failure of an oil temperature sensor according to a condition of a vehicle at an early stage, and to reduce incorrect determination, in a failure determining device of the oil temperature sensor.SOLUTION: A failure determining section (25) includes an oil temperature estimating part (25A) which estimates oil temperature (To0) of an automatic transmission (2) from an engine temperature (Te) to find an estimated oil temperature (Tx), a failure determination threshold value deciding part (25B) which decides a failure determination threshold value (C1) for determining that the oil temperature sensor (8) is out of order, and a failure index determining section (25C) which finds failure indexes (degree of failure (Cu), degree of normality (Cd)) being larger as getting larger oil temperature difference ( T) between the estimated oil temperature (Tx) found by the oil temperature estimating part (25A) and the oil temperature (To0) detected by the oil temperature sensor (8). When a count number (Co) which is sum of a plurality of failure indexes found by every predetermined period reaches the failure determination threshold value (C1), it is determined that the oil temperature sensor (8) is out of order.