service engine light on code P0125

Anyone ever get this code from thier car.
I looked up the code and it says insufficient coolent temp for CLosed loop fuel control.
Just wondering if some else has had this problem and what they did to fix it.
There seems to be plenty of coolent.
I am having problem with heat though.
Any thoughts would be great thanks.

thermostat? heater core plugged?

thanks for the reply Blaze.
Im working on a friends bmw.
Just replaced the radiator recently but he didn't change the thermostat.
Probably should have cause it was doing this before hand.
Hopfully its not the heater core cause it looks like a bear to change.

it may not be so bad to do a heater core on some modles, some of them come right out the firewall under the hood (SOME) lol hope you fix your heat man