Check engine light on

The code helps to point you in a direction. This can be from a bad sensor, bad wire, poor connection, thermostat etc. Here is some info about this fault: http://repairpal.com/OBD-II-Code-P0125 My experience tells me this is a thermostat, are you seeing that the engine is not warming up to operating temperature or it takes a long time to do so? If so, replace the thermostat and reset the check engine light. Good Luck