I have a 2003 Ranger with a 2.3L engine. While running I got a check engine light with temp gauge in the intrument cluster going full hot. I checked and got a P1299 code. This indicated the CHT sensor was in protection mode. The actual coolant temperature was not overheated when I checked and later when I started the engine in a cold condition the code threw again with the temperature gauge going full Hot (when it was absolutely cold). OK, so I will replace the CHT, I believe since it was in protection mode it was giving the computer the wrong fuel mix causing my engine to run rough also. I unplugged the CHT (until I install the new CHT) and the engine runs OK with a new P1280 code (expected since the CHT is unplugged) and the temp gauge inside is dead with no input and needle below the C position.

There are two sensors, one is the mentioned CHT sensor and the other is the ECT (Engine Coolant Temperature) sensor. The CHT signal goes to the computer and the ECT is supposed to supply the signal to the temp gauge on the instrument cluster.

Question 1 (Important): Does anyone know the correct torque setting for installing the CHT? I know it is a low setting because you can break off the threaded portion due to it being thin brass.

Question 2: Why was the temp gauge reading full hot as if the signal to it was coming from the CHT instead of the ECT sensor? The temp gauge signal is supposed to be coming from the ECT.

Question 3: Does the CHT override the ECT input to the temp gauge when it thinks the coolant is too hot?

Question 4: After I unplugged the CHT I got no temp gauge reading. Is this a condition of the possible override (question 3) or do I have a bad ECT also? Note: I got not codes relating to ECT.

I would appreciate any comments that help clarify this.
Thanks,

JIm

 

Did you ever figure out the problem I'm having same issue 2.3 2003 ford ranger I drive around 80 miles and temp gauge drops to zero has to be electrical my shop has tested all of coolant pressure and flow and everything is good new thermostat comes with sensor and replace the coolant sensor on back of motor even replaced cluster and still doing it I found that my wires are kinda stuck together like they are melted I tried pulling them apart but did more damage than anything found couple of bare areas but it was probably from me pulling them apart. Curious if you found the issue it might give me insight of what to look at next. Thank you very much