I got in my 2007 MCS yesterday after work and the yellow check engine lit up on the tach display for a couple of seconds. It was in a covered garage all day with below zero temps. After warming up and running a couple of erands it never lit up again. Should I be concerned or is just the cold weather? By the way, it is the first winter I have owned it.

 

was this a yellow triangle in tach display?
check engine light is in speedo.
probably the freeze warning you saw lights up for a few seconds
when under 37 degrees

 

Mine did the same thing the other day. I turned it on and the half power check engine light came on and made the car idle pretty rough. I let it sit for about 5 min hoping that it would come off and it didn't. I turned the car off and restarted it and it didn't come back on. Seems to be a known issue. Check out the stock problems forum, you'll find a ton of info about it in there.

 

Mine did this to me tonight. So far the light is still on though. I shut the car off the first time I started it because it was running really rough and couldn't figure out whether or not it wanted to run at half engine power or turn the check engine light on. Now the check engine light just stays on on the Speedometer. The car is running fine though....

 

You most probably have the "moisture freezing in the throttle body" issue. The check engine light on the speedo is on because the codes have been triggered. The ice thaws after the car warms up a bit. shut the car off and turn it on and it should run fine. Take it to the dealer and they can check the codes, clear them, and fix the issue under warranty. they have a new throttle body that is supposed to fix it. I erased the codes with my scangauge and have to duplicate the scenario sometime in the next 20k miles to get the dealer to fix it under warranty. So in a roundabout way, its good your CEL is still on.

 

If you don't like the CEL on (who does) you could take the car to Autozone and have them scan the codes and clear them for you (some will not do this though) or you could find a buddy with a scan tool to do it, just write the codes down and either check here or google them, that's what I did. My CEL stayed on but the car ran good, go figure

 

The check engine light has gone off and the car is running fine now. Tonight is supposed to be about -10 so we'll see how things go...

 

Mine was the manifold issue. The dealer knew immediately what was going on once I explained the issue to them. Now I'm just waiting for the dealer to call back.