I've been doing research for some time now and figured I would just make my own thread. I have an 03 Ranger Sport 2WD 5speed. CHT sensor has been replaced, thermostat has been replaced, radiator has been replaced, ECT sensor is working normally. Basically, after any short drive, the coolant temp gauge just makes it's way up to H. Sometimes it'll fluctuate up and down a little bit, but mostly staying in the H range. If I unplug the CHT, the gauge operates pretty much normal, with little fluctuation once it reaches op temp. AC doesn't work without the CHT plugged in, which sucks. I replaced one of the O2 sensors as it was rubbing against the new cat that was put in recently. I also added in a bracket to the exhaust to move it away from the tailshaft housing of the trans, which is what that O2 was rubbing on. Not sure what else could be wrong with this truck at this point. Any suggestions?

 

Welcome to the forum

Just to be clear you replaced the ECT SENDER<<< sender not sensor name really matters here
ECT Sender is used for the temp gauge in the dash
ECT Sensor is only used by the computer

They are also not interchangeable, sender uses 12volts, sensor 5volts

In 2003 the sender, sensor and CHT are all connected to computer, but only sender is connected to dash gauge
Its Red/white wire is spliced/split, one goes to gauge, other goes to resistor in engine fuse box and then to computer

You can unplug this resistor and see if gauge behaves normally, this would disconnect computer and CHT connection, with new ECT SENDER

 

I didn't replace the ECT Sender. I replaced the CHT sensor. The one on the top of the valve cover with the plug wires.

 

Then replace the ECT Sender if gauge is acting up

 

But the gauge operates properly when the CHT is unplugged. When it's plugged in, it spikes.