Failure detection device and method for automatic transmission

摘要

There is provided a failure detection device for an automatic transmission having a one-way clutch to disable engine braking in a given gear stage and an engine braking friction element to lock the one-way clutch and switching between a first shift mode in which the engine braking friction element is disengaged in the given gear stage and a second shift mode in which the engine braking friction element is engaged in the given gear stage. The failure detection device includes a failure detection unit that detects a failure in the automatic transmission based on a deviation between actual and target transmission gear ratios during non-shift operation of the automatic transmission and a prohibition unit that prohibits operation of the failure detection unit until a predetermined time has elapsed from switching of the automatic transmission from the first shift mode to the second shift mode.