Transmission oil type may be determined based on the opening time of a transmission latch valve and on oil temperature. An opening time of a latch valve positioned between an oil reservoir and one or more torque transmitting devices of a transmission is determined in response to a command to open the latch valve. A temperature of oil supplied by the latch valve from the oil reservoir to the one or more torque transmitting devices in response to the command to open the latch valve is also determined. The latch valve opening time and oil temperature are monitored over a range of oil temperatures to collect opening times of the latch valve at each of a plurality of oil temperatures within the range of oil temperatures. The transmission oil type is then determined based on the opening times of the latch valve at each of the plurality of oil temperatures.