Abstract: A diagnostic strategy for an automatic transmission having electronic shift control solenoids for controlling application and release of clutches and brakes during the establishment and disestablishment of torque ratios in multiple-ratio gearing for the transmission wherein provision is made for developing diagnostic data that detects failure modes due to a faulty shift solenoid by using predetermined failure modes stored in the RAM portion of a microprocessor and comparing those known failure modes to the actual performance of the shift solenoids.

Abstract: An automatic transmission having multiple-ratio gearing, fluid pressure-operated clutches and brakes adapted to establish and to disestablish multiple torque ratios and electronic shift control solenoids that can be energized and de-energized under the control of an electronic microprocessor that senses transmission operating variables, and a control strategy inherent in the microprocessor that uses predetermined failure modes to perform functional testing on the shift solenoids without special hydraulic and electronic hardware for developing the diagnostic information that detects shift solenoid failures or malfunctions.