Basically I just purchased a used 05 S40 T5 FWD about 2 weeks ago the car has been running great up intil today.
I was on my way home from work this morning the weather is crappy , heavy rain , I was using the Cruise Control going 100km/h when I caught up to the person in front of me who was doing about 70km/h so as I was approaching him I used the speed control to let off the throttle using the - on the steering wheel , I coast down to 70km/h suddenly the person in front of me starts going faster so I use the + to gain speed again , then he slows down I use the minus, then he speeds up I used the + but this time when I go to use the + all of sudden a message comes up on the screen saying Reduced Engine Performance , the cruise I believe auto shut off at that point pressing the pedal did nothing , so I coast it off the side of the road throw my 4 ways on and the car was idling really rough, pressing the pedal would not rev up the engine. So I shut the car down, leave it off for about 5 seconds turn it on again it started back up with no issues and then all my power is back and the message is not showing when I start the car but if I press the read button then I can still display it. But after restarting the car seems ok.

So yea I dunno if its the wet that got into something or something to do with the cruise control or what. All I know is I spent all my money getting this car and now Im scared its a lemon anyone else experience this issue?
Prior to this the car was running great.

 

So after a few days now of running it , it seems like the engine sounds im not sure of the word Bogey I guess on the highway and it seems to be not shifting or slipping when you try to accelerate fast but if you go easy on the gas the slip is not there. Everytime I start the car the message is still displayed unless I hit the read button to remove it. So im not sure if the slipping or trouble shifting is due to the engine or what. I was told by a mechanic that it was a safety feature with the car if the wheels slip then the car will cut the engines power and go into limp mode I still wanted the codes read but he never had a compatible computer. So I have to wait till the middle of the week for a friend at work to bring his in to hopefully get the codes.
I have such bad luck, I just got rid of my ride cause of tranny problems and now it seems I may have a way more expensive tranny problem on a car I owned for less then 2 weeks................

edit .... Forgot to mention the car was certified and has a 30 day saftey waranty, would a failing transmission fall into the safety warranty?


Edit.... How do I check the transmission Fluid on a 05 s40 t5 , I been looking around for 15-20 minutes trying to find the dipstick but cannot see it , in the owners manual theres no reference to where it is and google isn't helping me either

 

Does your S40 have a sunroof?

 

The dipstick is in an idiotic location. Stand looking down at the left side (driver's side) of the radiator, and it's down under all those hoses that block your view of the ground / splash pan. You can probably wrap your fingers around those hoses (as long as they're cold) and feel the dipstick, though I doubt you can extract it. And of course, you're supposed to check it with the engine and tranny at full operating temperatures, which means you need to be willing to get burned just to try (probably unsuccessfully) to get to the tranny dipstick.

That said, you mentioned that the car was running rough when this happens - no reason for that to happen if it's a transmission problem. The first thing to check on a car that misfires after trying to accelerate is the fuel pressure / filter. A clogged filter might allow you to cruise at a steady speed all day, but trying to push the extra fuel through the filter to accelerate might starve the injectors and cause the problems you're seeing. If you can get a monitor (ideally a VIDA style system) on the car, you'll probably learn more, but at the very least stop by one of the many auto parts store that will throw a "generic" OBD reader on the car to see if that will tell you anything.