Transmission shift with pressure controlled cleaning pulses

A method of freeing a stuck electrohydraulic valve of a transmission, the method comprising:

• commanding a series of first pressures to an electrohydraulic valve associated with an oncoming shift element of a transmission shift prior to an off-going shift element slipping;
• commanding a series of second, higher pressures to the valve for a duration of time responsive to an expected ratio change of the transmission not commencing and the off-going shift element slipping;
• and
• commanding a series of pressure pulses, according to a duty cycle, to the valve responsive to expiration of the duration of time and the expected ratio change not commencing.

A transmission comprising:

• a gearing arrangement configured to shift speed ratios by disengaging an off-going shift element and engaging an oncoming shift element;
• an electrohydraulic valve including an actuatable valve element configured to control an engagement state of the oncoming shift element;
• and
• a controller programmed to, during a shift of the transmission:
• in response to the off-going shift element disengaging and an expected ratio change not initiating, monotonically increase current to the valve to a maximum value to overcome frictional resistance on the valve element, and
• in response to expiration of a timer and the ratio change still not initiating, send a repeating pattern of high and low current signals according to a duty cycle to overcome frictional resistance of the valve element.