Here is the situation. I filled my Tank up with the care running and the next day the CEL came on. Car running well no change in gas milage, wa very cold this past week but not sure if this had anything to do with it.
P0128-Coolant thermostate
P0456 Evap leak detected

Why would the 2 of these code pop up together? I have driven the car over 700 miles since the CEL came on hoping it would clear but i has not.

Any ideas of what I need to do here. Thanks in advance here for your time spent.

 

I doubt that they are related as they are two different systems. The P0128 is likely a bad thermostat. The P0456 may be a bad EVAP control valve, bad fuel cap, loose fuel cap, leaky evap hose, or bad evap canister.
Stan

 

P0456 You dont think it was caused by fueling while car running. Just odd that the codes came at same exact time

 

Well, yes it will for the P0456. The system is checking for leaks while the engine is running. If the cap if off or loose then it will see this as a leak and flag a code. For safety reasons alone you should always turn the engine off while fueling. There are likely signs on the gas pump and warnings in the owners manual saying the same. (I was going to give you a face palm but I decided not to).

I still don't think that caused the thermostat code though.
Stan

 

I never fuel with car running but it was very cold that morning and I left my coat at home (-10) Thanks for the reply, wil get the Thermostat changed and codes cleared. I live in NYC atthis time so do not have a place to work on car, will have to take it to dealer. Anyone know a fair price for this repair??

 

Thermostat is cheap and easy.
I think I paid <$100 for replacement.

But they may charge you to clear the codes, my dealer sometimes does..

 

They are charging 89 for fluid change, thermostat and clear codes. Thought it was a little high but Pepboys wants 192 in Queens.

 

220 is the total

 

I have 2 Volvo's and both throw EVAP codes after refueling. I have done everything by the book, replaced the gas cap and the vacuum hoses and still that pesky code comes along with, pretty much, every tank of gas. I bought a little $79.00 Actron pocket scanner in both cars so I can reset the computer after the CEL comes on. That way when you really need to know a code, you won't overlook it because you are assuming that the CEL is on due to a fueling code. It's a hell of a lot cheaper than buying and installing a new EVAP system. Good luck, Volvo's are very sensitive critters when dealing with EPA system functions.