550 slow down light

I'm not sure about the 550's, but on the 348's the slow down light is for the catalytic converter temperature. It gives you the slow down light when the temperatures of the cats starts to get too hot. It will go into the limp mode to prevent the cats from over heating. However, a very comon problem with the 348's is that the cat temperature ecu's will go bad, giving a false reading to the engine management system, resulting in the one or both banks being shut down. Depending on what bank of cylinders the ecu is getting the signal from. What some have done is to just disconnect the cat ecu's, and that has eliminated the bad signal to the engine ecu's. But, since you have a 550 I don't think it will be that easy to just get rid of the cat ecu signal. If your car has cat ecu's what you can do is swap them from one side to the other, and see if you get the slow down on the other side of the engine. If you do then you know that you have a bad cat ecu. Another possibility is that you have a thermocoupler going bad on you. That is the part that actually measures the temperature of the catalyitic converter. If you have one that has gone bad it will cause the engine to do what it did. You can pull the codes from 348 ecu's without a reader, but I don't know if you can do the same with a 550. You will need to see what codes your ecu has stored in it, and that will lead you to what caused the check engine light to come on. Wish I could be of more help, but I don't have a 550. Oh yeah one other thing, since you said that it felt like the car was missing, that could be what caused the slow down light to come on. If the cylinders weren't firing properly you will get unburnt fuel going to the cats causing them to get hot faster. So a misfire could be the cause of your problem. You know what, if you car is still under the warranty I wouldn't mess with it at all. Just take it to the dealer and have them fix it on their dime. Thats what warranties are for. So that if something does go wrong with the car, like it is with yours, before the warranty is up, you don't have to pay to get it fixxed. Hope I was of some help.