Engine light just came on this afternoon, checked the code, one was P0128 which I also had last year in the winter. Its for the temp not reaching thermostat regulating temp. The second one which is the one Im worried about is P0456 said something about evap emissions control leak (very small). Any ideas or thoughts for what this one could be for?

 

Here's a possibility. If the thermostat gets stuck open, then the coolant would flow freely and would never make it to the proper operating temp. The proper operating temp is critical for newer cars with emissions as it relies on coolant temp reading for entering closed loop i believe. If my memory is working correctly ( tell me if its not) the car runs in open loop mode until it reaches the proper operating temp then goes to closed loop. Closed loop is where the O2 sensors and other sensors start monitoring the engine for fuel mixtures and other items. With you being in a cold climate and the possibility of the thermostat not closing all the way, that is entirely possible. How's your fuel economy lately? Oh I'm no certified mechanic but I work on everything I have. I'm sure others will chime in and correct me if I'm wrong. The second code may well have something to do with the first so I'd try to clear up the first one and see if the second goes away.

 

Fuel economy was a little lower than normal but not terribly. I talked to a mechanic I know and he said to check the gas cap and reset the codes and see if they come back. did that yesterday and drove about 200miles between yesterday and today. Havent had any codes come up yet so I guess we'll see what happens

 

The EVAP thing was an issue I had on a 99 Passat about 3 or 4 years ago. Eventually got so bad it threw a code and my car wouldn't start after fueling. Ethanol had deteriorated the seals and the valve was stuck open and never closed to build pressure. in the system after I opened my gas cap. replaced it and no more problems after filling up.

First code is usually a bad thermostat