I've read just about everything I can get from the search on this part and I had a couple of questions. I have a 2002 F150 5.4 and I have been having problems with the truck not starting once the engine is warm. The engine starts right up when it is cool but once it is running warm, the engine idles very high. After some research and noticing the temp gauge was no longer working I went ahead and flushed the coolant and also replaced the thermostat. Since the truck is still doing the same, I concluded the sensor must be bad. Before going through the PITA that it is to change the sensor I wanted to see if there was any other possibilities to why the engine is acting this way.

I've read that the only way to replace the sensor is removing the alternator and intake, so I wanted to see others input before going ahead with that PITA.

Any help or suggestions are greatly appreciate. Thanks

 

By the way, the exact code being thrown is:

P0125 Insufficient Coolant Temperature to enter Closed Loop

If that helps at all.

 

You terminology is incorrect.
The Cylinder Head Temp sensor shouldn't be your problem. Your Engine Coolant Temp sensor may be bad. It is located in the front of the intake manifold opposite the thermostat housing.

 

ONELOWF, are you sure about this? I thought that model year had only the CHT sensor and coolant temperature was inferred from it.

Regardless, I think the faulty sensor diagnosis is correct. I'd replace it and see what happens.

- Jack

 

This is basically the reason I have been inferring others opinions. From what I understand, after 2000 the motor went strictly to a CHT sensor and not a coolant temp sensor. Either way, I believe it is the sensor that is my problem but further information and opinions are greatly appreciated.

The sensor opposite the thermostat housing (whether that is the Coolant sensor or not) is directly connected to the cylinder head sensor around the #7 cylinder within the valley, under the intake. Furthermore, autozone only lists a part labeled as "Coolant Temperature Sensor" and not a part labeled "Cylinder Head Temperature Sensor". Thus the reason for my confusion.

 

is it just giving you problems trying to start or is it not starting at all? if its just giving you problems than it sounds about right that the cht is no good and is causing the computer to dump more fuel into the cylinders.
does the sensor look like this?
http://www.napaonline.com/MasterPage...erature+Sensor

 

Now that you mention it, No I'm not sure. I thought that the CHT inference began with the 04's. But maybe not.:o

 

Basically, in order for me to start the truck if it is warm I have to crank it and then push the accelerator to the floor. That's the only way to get the thing started.

The sensor is tapped into the cylinder head, screwed in with a harness plugged into the top of it.

 

The ECT Sensor took a hike in 2002, in both 4.6L and 5.4L modulars. The 01's have them. After 2001, the CHT ran the show - took over the ECT's job via written program command for CHT to now cipher.

However, the 4.2L's still had them in 2002.


I'm pretty smart aren't I

- Not really - I have the 2002-2004 Ford Service (EVTM) PC/ED running , two computers down from this one. I just looked ( :

 

After 2001 is when they pushed the ECT out. Also 2002 is when they used the goofy looking DPFE sensor that's looks like no other.

I had a 2001 for awhile, that had a ECT. That was a 5.4L. I have a pic of that somewhere.

__________________________________________________ ______________

Alright, you have two separate problems IMO -

Crank No Start when warm -

The Fuel Pressure Regulator is not checked by the PCM (No wires right?) . -The Fuel Trims would have generated a DTC eventually, but these need a LTFT lower than perhaps -25% and a STFT lower than perhaps -5% before it would have recorded a negative Fuel Trim DTC. I've helped w/warm start issues in the past, on occasion.
If your CHT sensor is at fault - it's a news to me. When that sensor goes bad, it doesn't cause a crank no start issue that I ever heard off. What it can cause is "limp mode" activation, but she starts and will run, just not good to put it short.
You also mention a high idle when warm. This confirmed the regulator as the problem for me. A bad regulator will allow the fuel rail to over pressurize (where the high idle is coming from) - Test the rail while it's idling high and I'll bet it's @ 65 lbs or more.

Change your fuel pressure regulator on the rail (it's over there by #6 & 7)

__________________________________________________ _______________________________________

PO125 -

Here's what Ford does by the book (Sub in CHT for ECT in data sheet) -



__________________________________________________ __________________________________________________ _____________

If you do decide to change out the CHT - service procedure is to remove the manifold actually, not the alternator, BUT! I haven't changed one myself , I seem to recall another individual changing one out that was able to reach the sensor without taking the top end all apart. There is a hole there where you can reach in and get your hand on the sensor and I'm purdy sure it threads out like the old ECT's. Try to get a wrench in there first before dismanteling if you decide to change it. Also, if removing the alternator would give you the access you need, that's an easy job compared to the manifold.

Here's the hole on a 2001 model -



Here's a couple ECT Sensors. The CHT looks similar -



Good Luck .

 

2005 F150 CHT is under intake manifold on the passenger side of block. I had a mouse chew through both wires all the way to the connector. In the process now of removing the manifold to get to wire bundle for repair and replace. Can't post the pic.

 

2005 F150 5.4 Triton. CHT shown under intake manifold after mouse had chewed through wires clear to connector. (Loose wire bundle shown to the left of connector.

 

I got the connector pigtail out of the back-side of the manifold without removing the intake. Soldered the wires together and attatched the pigtail to the sensor with no problems. Should be ready to fire up this afternoon.

 

Thanks for to all for the great info.

I have a 2004 F150 4.6 V8. My gauge in the dash doesn't move from cold except for a time when I got the running temps up and shut the engine of and started it back up. This was the condition for about 2 month now it isn't working at all.

Runs great no codes after cleaning the TB and clearing learned Idle values. Heat and air works great so I am thinking it may be the gauge in the dash.

I guess before I replace the gauge, if possible, would the CHT cause this by not sending the correct signal to the gauge? Also if I do not repair is there a warning light if the engine starts to over heat?

 

@jvreed


This is an old thread, but I notice you posted just yesterday. Beware of a mix-mash of mis-information above. I have a 2004 v8 (5.4) and have replaced intake manifold. I can tell you the CHT is underneath the manifold - on the inside of the head between cyl 3 & 4, and is a Bitch Kitty to get to. Ain't nobody changing that damn thing without removing the IM - unless, possibly, you remove the hood, dashboard, windshield, and cut a 2'x 2' hole in the firewall in front of the passenger seat! I'm not sure the gauge is a much easier task to just try.


Seems to me to be a classic case where more diagnostic data would be helpful. It is often very difficult to diagnose these vehicles without a scanner. I would recommend getting a reading from OBDII system to see what the ECU "CALCULATES" as ECT (coolant temperature). If that's normal, it's most likely the gauge not able to respond to the ECU's commanded temp reading or an instrument cluster problem. If it's not normal, its most likely the CHT or wiring from that direction. - And 'no', there is no warning light. But the ECU will put the engine in limp mode (alternating shutting down 4 cylinders fuel injectors), at which point you will think it has totally cratered.


There are several decent options for obtaining OBDII scanner data relatively inexpensive these days. I use the Torque Pro app ($4.95) on my Android cell phone - and it gives ECT and 'tons' of other useful data.


Good Luck