I got the PO125 Service Engine Light Code again. About a month ago I got the code and I had it reset and the truck has run fine.

Yesterday, I got the SE light again and the code again is PO125, Insufficient Coolant Temperature for Closed Loop Fuel Control.

I presume there is a temperature switch somewhere that triggers this thing. Does anyone know where this sensor is?

Autozone lists a temperature sensor and a temperature switch. Is it the switch? The temperature indicator works the same as always. My truck is a 2000F150Scab4x4 with the 5.4 engine.

 

Two possibilities, the engine really isn't warming up enough and fast enough. This would usually be thermostat related. The other possibility is that the computer isn't reading the termperature correctly, which would be the sensor, the wiring, or the computer.

There are two possibilities, they used to use a ECT or Engine Coolant Temperature sensor but they converted sometime around your truck to a Cylinder Head Temperature CHT sensor. It is on the head below the intake but can be changed without pulling the intake manifold.

Another possibility is that you have exhaust getting into the coolant through a head gasket or cracked head putting a bubble over the ECT, which would then just record the intake manifold temperature. This wouldn't be possible with a CHT type sensor.

 

Check out:

https://www.f150online.com/forums/sh...hreadid=185614

SL

 

Thanks for the replys.
I took it to the Ford Dealer today and their diagnosis was the engine wasn't heating up fast enough and it needed a new thermostat.
I'm skeptical because according to the temp indicator it appears to heat up the same as it has since the NEW oversize radiator was installed 3 or 4 yrs ago. The first time I got the SE light I had driven about 30 minutes and was traveling on the interstate at 72mph. The wind was blowing like crazy and it was in the 20's. The second time I was leaving a store after parking for 30 minutes or so. The temp was 47 degrees outside.
Since the new free oversize radiator was installed, the engine does not heat up as much or as fast as before, but like I said, that was several yrs ago and I have worked in the frozen north every winter since then.

I suspect a rusty electrical connection.

My next step is to put some card board in front of the radiator.

 

Readings from the temp gauge and the actual reading from the ECT can vary as much as 30 degrees or so.

 

You have run into a marginal situation by using a larger radiator.
The PCM software is complex in how it handles this.
It involves intake air temp, the thermostat assuming it's operating at it's designed opening temp, a PCM timer.
The DTC code will be set and a lite come on if the temp has not come up to 175* within 300 to 800 seconds after startup
Consider that a larger radiator holds a larger volume of coolant and will in most cases make the thermostat open and close at a faster rate while still mantaining the block temp.
This by itself could be a wear factor on the thermostat causing it to allow more coolant to flow and making the system run at a lower temp such that the PCM detects this.
The PCM programs are written and calibrated to work with factory determined parts performance. Some times making changes gets a part of an overall design out of calibration.
I would also agree that the thermstat should be changed as a first step.
You may refernce page 38 of the Ford OBDII manual on Thermostat operation and code P0125.