I have a question I was hoping yall could help me with. So I have a 2002 Ford Ranger 3.0 2wd. For the past two months my temperature gauge has been stuck on cold. Naturally, I replaced my thermostat, temp sensor as well as the coolant temp sending unit. Gauge still stuck on cold. Starting to feel pretty overwhelmed, any idea what I’d could be? Also my check engine came on and the code read P0125. Starting to think maybe my wiring is bad? Please help

 

Welcome to the forum

How is the heat in the cab?
Should be very very HOT after 10minutes of driving

As you know there are two different Temp units on the engine
5volt ECT sensor, only used by the computer
12volt Temp Sender, only used by dashboard gauge
So very different devices not interchangeable

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
This is because the ECT sensor is reading a low temp(under 150degF) after 5 minutes or so of engine running


Temp sender always has a red/white wire, if you unplug the sender connector and GROUND the red/white wire, then turn on the key, the Temp Gauge should go up all the way to HOT, if so then red/white wire and gauge are OK
Sender may also have a Black/white wire, that's the sender Ground wire, so jumper the the two wires together and repeat the test
If gauge doesn't go to HOT in either test then red/white wire is disconnected somewhere, maybe a gauge issue but wiring is more likely
But nothing to do with code P0125

Having BOTH P0125 and low or no temp on dash gauge would point to a thermostat issue, new or not
But very easy test for that
Start cold engine
Feel heater hoses at firewall and the upper radiator hose, they are all cold of course
Let engine idle 2 minutes or so and feel the hoses again
Heater hoses should be warming up, upper rad hose should still be stone COLD
If upper rad hose is also warming up then thermostat is open and it should be closed

Thermostat prevents coolant flow thru radiator until engine coolant is above 185degF, in winter months radiator may never be used

 

Good afternoon Ron,
I wanted to ask questions regarding the ECT Sensor & Sender. I got a check engine light on my 2002 Ranger 3.0, the diagnostic tool advised the code was for the ect sensor. From what I see online the sensor has the cone tip($60) and the sender has a cylinder tip($15) when I replaced the sensor (next to the thermostat housing,,, with 2 wires) a cylinder tip sensor came out, I replaced it with a cone tip sensor, and when I finished and started the truck the check engine light went out by itself and my gas mileage is back to normal(thank God!) When I took the "Sender" out of the truck, it had the cone tip sensor in it, so I replaced it with the cylinder tip sensor, ANYWAY, Long story short is im very CONFUSED!!! It looks like those sensors were installed on my truck backwards, I should've just replaced the cone tip with a cone tip and cylinder tip with cylinder tip. Anyway, now my sensor is working, but I'm not getting a reading on my dash, it looks like the needle is moving a tiny bit, but its not getting off of cold after running for 20 mins or more. The temp gage was working before I replaced both sensors but now the sender isn't working. I went back to parts store and bought another $15 sender, I was thinking maybe the 1st sender i bought was defective but the new sender doesn't work either. My whole plan was to fix the "sensor" and while I had the coolant all drained I figured I would replace the thermostat, gasket, and "sender" all together, but now I'm still working on fixing the sender. I was gonna try the trick you advised about grounding the wire to the negative battery terminal, & turn the key to on but don't crank, to test and make sure the gauge still works, but I'm not 100% sure how to use a jump wire the way you are explaining. Also, should I just go back and buy another sensor(Cone tip) & install it on the connector that i currently have the cylinder tip sensor on? It has the 1 wire. If I didn't confuse you, can you please help me? The truck has run great the last 8 years I've had it, even though those sensors were installed backwards on the truck. If I buy another $60 sensor(cone tip) and it doesn't give me a temp. reading on my dash, I'm debating on taking the truck to a repair shop,, however I rather not go that route & fix it myself, if I can.

 

All started with replacing the broken heater hose, I planned on flushing coolant and replacing the thermostat. When running the engine during a water flush I noticed the temp gauge never went above cold after running for 20 min. I currently don’t have the thermostat in (to get a good flush) but it should still register temp going up as it runs. I replaced both the temperature sensor and sender, I also did the sender grounding test for the gauge and it went up to H. But when everything is plugged in it still registers below C and doesn’t move.
I heard someone say the grounding test isn’t exact so the gauge could still be the problem or I’m thinking maybe the clip on the sender wiring if it doesn’t make decent contact or possible rusting in the threads in the engine portion. Can’t wait to hear any suggestions, thanks in advance.