Diagnostic code definitions & solving them on 2004 mazda 3
 

:wave:Code P0128 and 126 say the input from coolant temp sensor says a temp value that is below the thermostat regulating temp.
(Coolant temp is always low but the powertrain sensor verifies that the engine temp is correct. ECT sensor defective and cost to replace...

Code P0455 says a large leak exists in the evaporative emission control system. Lists several possible causes... defective fuel cap (seems O.K. to me), EVAP cannister broke, hose cracked or not connected (Could "Oil change guy" have pulled off and not reconnected?) Purge or vent solenoid defective or vacuum leak at engine detected.

Anyone have experience with any of this or offer cost estimates and or other helpful info?

No idea on the temp. other than a possibly bad thermostat. For the evap. code make sure your gas cap it on tight (turn until it clicks several times) as that can throw that code. Also if you've not had your purge valve/solenoid replaced then that could also cause the evap. code. They had a bad problem with the purge valves in '04-'05 cars. I actually went through four (under warranty thank god).