Abstract: A method of diagnosing a lock-up mechanism for a torque converter in an automatic transmission of an automotive vehicle includes the steps of sensing vehicle speed and engine speed, calculating a vehicle speed to engine speed ratio based on the sensed vehicle speed and engine speed, knowing when the torque converter transitions between unlock and lock are initiated, determining whether the calculated ratio is greater than a predetermined threshold when the torque converter transitions between unlock and lock, and concluding that a failure of the lock-up mechanism has occurred if the calculated ratio is not greater than the predetermined threshold within a predetermined time since transition of the torque converter.

Abstract: A method of diagnosing an idle speed control system for an internal combustion engine in an automotive vehicle includes the steps of determining whether a plurality of conditions are met for the idle speed control system, ending the method if the predetermined conditions are not met for the idle speed control system, determining whether a difference between an engine speed and a target idle speed is greater than a predetermined threshold value if the predetermined conditions are met for the idle speed control system, and concluding that the idle speed control system is functioning properly if the difference is not greater than the predetermined threshold value.

Abstract: The status of a Park/Neutral (P/N) switch for an automatic transmission in an automotive vehicle is diagnosed by a method which includes the steps of determining whether an engine of the automotive vehicle is cranking, diagnosing the P/N switch for a P/N state of the automatic transmission when the engine is cranking, and diagnosing the P/N switch for a Drive state of the automatic transmission when the engine is not cranking.