Water coolant gauge is not reading any temperature, Replace the water coolant sensor next to the Thermostat

2001 Dodge Ram 2500 with 5.9 Diesel.

performed gauge test procedure and coolant temp had movement just as the other gauges.

Can a bad thermostat cause for no reading on the water coolant gauge in the instrument cluster.

 

Sure. It doesn't start "reading" until about 130 when the needle starts to move. If it isn't getting to that it won't show.

 

Check the sensor wire too for continuity and resistance

 

Does the diesel have a separate one-wire sensor for the gauge? Or does it get its cue from the PCM, like the rest of the gauges?

 

the gauge worked during the self test

 

So knowing where it gets is signal from is important.

 

The test is just that, A test to see if the gauges move. You issue is the signal is not getting to the gauge. As HayYou said you need to see if the signal comes direct from the sensor or goes into the pcm then to the gauge.

 

2001 dash instruments are all computer controlled by the PCM. However on the diesels there is another module named ECM, engine control module. It talks to the PCM and from what I can tell it has the ECT sensor connected and relays the info to the PCM. So check the sensor readings, the wiring and look with a scan tool what the computer thinks the engine temp is. If it's really low (-40F or similar) the sensor/wiring is broken. If it's just cool it might be the thermostat.

 

I can not find the wire circuit that the ECM relay information to the PCM... I wonder if both ECM and the PCM monitor the Coolant temperature I did find the PCM monitor the Engine coolant sensor and send the signal to the instrument cluster.. but I could not find that circuit in the diagram on my CD

 

If your oil pressure gauge works then the communication between the ECM and the PCM works. 8W-30-40 in the factory service manual shows the CCD connection between ECM and PCM.