My '05 popped up with this CEL a week ago. I got it read at Autozone and they told me it was either low coolant, a bad thermostat, or a bad coolant temperature sensor. I was due to change the coolant anyway, so I changed it and the light remained on. I disconnected the battery and left the car overnight and the CEL didn't come on again for another couple days, but when it did, it was the same code.

I imagine it's not the CTS as the ECU would immediately detect some kind of bad connection and it wouldnt take days for the CEL to come on? So I guess I'm going to replace the thermostat as it seems to be the likely culprit (and the cheapest I'm guessing).

So I guess my question is, am I going in the right direction here?

 

Well, I didn't get any replies, but I thought I'd post the results so far.

Replaced the thermostat and taken the car through 3 warmup, drive, and cooldown cycles with no return of the CEL so far. So looks like the thermostat was the problem.

I will add that it was a pretty big pain in the **** to replace though. Better than paying the dealer to do it though!