We have gone through a cold snap here in Georgia and I noticed a little bit of a pattern in the check engine light. It stays on constantly during warm weather, but when it gets below 45 degrees at night the light doesn't come on after a cold start until the engine reaches the normal operating temperature. There seems to be a "sweet spot" of sorts as this only happens when I start the car cold and the outside temp is somewhere between about 30 and 45 degrees. I the outside temp is warmer or colder the light pops on about 10-15 seconds after starting. I had the timing belt replaced at 60k miles (it is a 5-speed).