2009 sonata 2.4 .auto tran problem
 

When the transmission is cold for like the first 5 to 10 minutes of driving when I'm slowing down and I get to 20 mph the transmission down shifts hard. Its always happens at exactly 20 mph when slowing down. It does not happen when accelerating. Once the transmission warms up it does not do this, It works fine. As soon as the transmission cools down a little it does it until it warrms up. As long as I keep driving it works fine. Anyone have any ideas.

History? Has it always done this? Did this just start? Was the transmission ever serviced? Mileage?

I would definitely suggest by answering these questions first but if you do end up needing a transmission we have a new one available, part number 45000-3A235 (available here: AUTOMATIC TRANSMISSION ASSEMBLY & TORQUE CONVERTER ASSEMBLY made by Hyundai. #450003A235). We also have a remanufactured version available, part number 00268-3A235 (available here: AUTOMATIC TRANSMISSION ASSEMBLY & TORQUE CONVERTER ASSEMBLY made by Hyundai. #002683A235). These transmissions are not cheap to ship but we typically save you money even when the shipping is calculated.