You could scan it. There's three types of codes. Current, History and Immature. Immature is when it takes say 2 drive cycles for the light to to kick on.. well one cycle is considered immature. History..should be all history. Current..only stuff that has the light on at that second.

Current trans codes typically are reset with ignition off. If you want to scan them, don't turn the car off. If the trans shifted super firm/hard then that was P1811 aka the typically pcs code.