Before changing my coolant thermostat the car didnt want to shift properly when it was cold, but i could force it to shift by pushing the "Winter mode" button. Now that i have changed the thermostat the shifting problem no longer occurs when cold. Now after the vehicle is warmed up it has the same problem, but it works properly when its not warmed. Anyone have any idea what would be causing this

 

why did you change the thermostat in the first place? the thermostat is a mechanical switch so it seems you have something temperature related - ie an issue with a temp sensor (on the S40 the ECT is directly below the thermostat cover) or the transmission is heating up thinning out the fluid (but that should throw a code). Did that get replaced as well? To rule out dirty fluid, you can do a drain fill or a flush. Otherwise It could be the PNP switch or one of the solenoids acting when warm.

 

There is a cooler in the transmission cooled by the coolant so the engine temperature has a direct effect on the oil quality.When the oil is cold the tranny will shift hard and late when it gets warm it should shift just right.If it does overheat you'v got problems.At this point I would also suggest a full flush but before you do that open the coolant reservoir and see if its clean or if you see murky/oily stuff in there.If you do then the cooler in the tranny is leaking.

 

My reason for changing the thermostat was i had a code for it being open under the required tempurture, took it out and it was wide open so everything was cold for an extra 20-25 minutes