Method of discharging transmission accumulator

A transmission comprising:

• an accumulator selectively fluidly connected to a line pressure circuit;
• a first shift element apply circuit alternately fluidly connected to the line pressure circuit and to a vent;
• a controller programmed to
• drain fluid from the accumulator by repeatedly partially filling a first apply chamber via the first shift element apply circuit and then venting the first apply chamber until no increase in clutch pressure is detected,
• in response to an accumulator discharge request, partially drain the circuit, and
• in response to a park valve not moving, completely drain the accumulator with the first apply circuit fluidly disconnected from the line pressure circuit.

A method of draining fluid from a transmission accumulator comprising:

• repeatedly
• operating a shift valve to fluidly connect a shift element apply chamber to a line pressure circuit;
• opening an accumulator control valve to fluidly connect the transmission accumulator to the line pressure circuit to partially fill the apply chamber;
• and
• operating the shift valve to vent fluid from the partially filled apply chamber
• until no increase in clutch pressure is detected;
• in response to an accumulator discharge request, opening the accumulator control valve with the shift element apply chamber fluidly disconnected from the line pressure circuits;
• and
• in response to a park valve not moving, leaving the accumulator control valve open with the shift element apply chamber fluidly disconnected from the line pressure circuit until the transmission accumulator is completely drained.