I went to autozone to get the code to tell me why my check engine light is on. P0125 was the code, "Engine Coolant Temperature [ECT] Excessive Time To Closed Loop Fuel Control". This is on an 2002 Ranger. Now I checked coolant level, that was fine. I removed the radiator cap and there was fluid to the top, so I dont think that is the problem. I took the thermostat out and put it into a pot of boiling water and it was working. I then took out the temperature sensor. I measured the resistance on it in ice water, room temp water, and hot water. I was able to get a reading as high as 4 kohm in the cold water and under 1 kohm in the hot water. So that appears to be working, though I do not have a spec on it. So now I am left scratching my head. The light is still on. By the way there has been no overheating. I assumed this was due to an electronic fan that was working overtime. Any ideas?

 

Put a thermostat in it.. The code has to do with the time it takes for the thermostat to open. You test proves that it will open, but it may take too long.. Thermostats are very common on , pretty much, all Fords , Focus/ expedition and others.. Good luck!