Hi guys. First post here...

I recently bought a 2000 Mazda b2500 down in Florida. I drove it back up to New York where I live. The CEL came on as soon as it got cold out. My code scanner reads P0125, “Insufficient Coolant Temp”.

The gauge on my dash was showing that the engine was running very cold, barely getting above the C. It was showing normal running temp when it was warm outside. So, I assumed that the thermostat was stuck open.

Replaced the thermostat, cleared the code. The code came back after about 150 miles.

So i thought maybe the sensor was bad. Changed the ECT sensor, and the sending unit for good measure. The gauge on my dash started reading normal, warming up to right below halfway! Weird..

Cleared the code, and it came back on again.

I’m at a total loss as to what to try next. Any thoughts??

 

When you replaced the ECT sensor did you use any thread sealer like teflon tape? If so that will cause a problem. The sensor needs the bare threads for grounding.
You can also check the wiring from the ECU to the sensor plug. Disconnect the plug from the sensor. With the key on engine off you should have 5 volts on one of the wires (I forget which color it is) this is from the ECU. The other will be a ground from the ECU. This will at least let you know your wiring is OK.
If you get a blutooth OBDII scanner you can see the actual numbers. Just down load the app. I have the Jethax scanner and use the Car Scanner app on my phone.