P0125 in a 2001 Ford Ranger

So here are the symptoms:
P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control
Heater does not work, well it works on a hot day, not on a cold day.
Temp Gage on dash does not read anything, sits at below COLD.

For what I read the possible solutions are:
Check Coolant Level - Done
Replace Thermostat
Replace Coolant Temp Sensor

More Info:
I've reset the light before and it comes back within the week.
Its been this way for over a year.


ANY HELP!?!


Thanks
~Rob

so you haven't replaced the the thermostat?

Nope, no actions yet except reseting the SES

Well then flush the coolant, replace the thermostat and rad cap and check the cooling system for any leaks or combustion leaks, like a blown headgasket, but likely you just have a thermostat stuck open or a rad fan that stays running all the time! Buy the thermostat from your Ford dealer to be sure that you get the correct heat range because too cold a thermostat rating will trip that code and give you poor heat output, flushing your heater core wouldn't be a bad idea either!