The CEL light recently came on while I was driving so I scanned the code with a scanner.
The code came out to be “18613 / P2181- Performance Malfunction in Cooling System”
I ignored this issue for a few weeks and noticed the CEL light went away for a time but as soon as the outdoor temperatures dropped down the light would come back on.
The issue was the thermostat in this case, especially considering that when the outdoor temperature changed, the light would come back on.
To fix this issue, simply replace your thermostat.
The procedure is not too complicated. Simply drain the coolant and remove the thermostat. The hardest part is removing the bottom bolt on the coolant outlet connection.
Normally I’d post a more in depth guide but I found a nice video on YouTube that will show you exactly what to do: