2002 dodge diesel Temperature gauge not working,have changed Coolant temperature sensor, still not working

I think the temperature sensor and the coolant fan switch are two different sensors. One tells the temperature and passes it to the ECM which passes that information to the gauge, the other works via a relay to turns the fans on and off. A fan spinning freely is not a test. You need to connect it to 12 volts and watch it run.

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Yes no problem.

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Did you change the coolant recently?

An air pocket many be trapped on the top of the coolant sensor.

Try to locate a small air purge bolt near the coolant temp sensor.

If you can not find it then just back off the sensor and let some coolant to come out.

Please have container and shop towel to catch the coolant.

The goal is to purge the air pocket.

Please make sure it is level and engine is cold when you do this procedure.

Could be your coolant temperature sensor is bad.

2003 Dodge Neon (non-Turbo)

The coolant sensor threads into the rear of the cylinder head, next to the camshaft position sensor. New sensors have sealant applied to the threads.

The ECT Sensor is a Negative Thermal Coefficient (NTC), dual range Sensor. The resistance of the ECT Sensor changes as coolant temperature changes. This results in different input voltages to the PCM. The PCM also uses the ECT Sensor input to operate the low and high-speed radiator cooling fans.



The combination coolant temperature sensor has two elements. One element supplies coolant temperature signal to the PCM. The other element supplies coolant temperature signal to the instrument panel gauge cluster. The PCM determines engine coolant temperature from the coolant temperature sensor.

As coolant temperature varies the coolant temperature sensors resistance changes resulting in a different input voltage to the PCM and the instrument panel gauge cluster. When the engine is cold, the PCM will provide slightly richer air-fuel mixtures and higher idle speeds until normal operating temperatures are reached.

The PCM has a dual temperature range program for better sensor accuracy at cold temperatures. At key-ON the PCM sends a regulated 5-volt signal through a 10,000-ohm resistor to the sensor. When the sensed voltage reaches approximately 1.25 volts the PCM turns on the transistor. The transistor connects a 1,000-ohm resistor in parallel with the 10,000-ohm resistor. With this drop in resistance the PCM recognizes an increase in voltage on the input circuit.

Sound like a ECT (engine coolant temperature) sensor go to bad or out of range.

you are correct as a single blade connection is mostly the temp gauge sender as the gauge grounds out through the variable resistance in the sender unit
most coolant temp sensor units have 4 wires in a square shaped plug and are generally in the same vicinity
I am at loss as to any transmission problems coming from a coolant sensor problem as the purpose of that unit is to report the engine coolant temp so that the ECM can adjust the air/fuel mix, turn on the radiator fans
There may be an transmission temp sensor to report to the ECM when the transmission overheats and that would put on the engine light
It appears that the recurring problem has again surfaced
but check harness connections for corroded pins , water ingress, and check the transmission control module for connections and operation
you may also check the vacuum actuator and hose for leaks and correct operation as that unit will attempt to change ratios as the throttle setting alters

According to Autozone.com:

Because ECT (engine coolant temperature) sensor procedures vary depending upon their location, first locate the part. You may need to partially drain the engine coolant to prevent coolant spillage.

• Disconnect the negative battery cable.
• Unplug the ECT.
• Then, unscrew it.
• Reverse the removal procedures to install the new part.
• Connect the negative battery cable to the battery.

Related Parts:



Cooling Fan Switch
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Engine Temperature Sensor
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Temperature Switch
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Coolant Temperature Sensor

Fig. Remove the coolant temperature sensor
The coolant temperature gauge sensor is a temperature-variable resistor, or thermistor. As coolant temperature increases, the resistance of the sensor decreases or decreases, depending on the type of sensor.
A1 and A2 platforms use a different type of circuit that A3 vehicles. On A1 and A2 vehicles, the circuit is a "resistance to ground" type. A3 vehicles use a "variable voltage" type, where a voltage is supplied to the sensor. Because of the circuitry design on A3 vehicles, testing of the coolant temperature gauge is limited.
The engine coolant temperature gauge uses a heat sensitive sending unit to transmit an electrical signal to the gauge. The sending unit is a heat sensitive variable resistor that is located on or near to the cylinder head and threads into an engine coolant passage. The sensors are a Negative Temperature Coefficient (NTC) type. As the temperature increases, the electrical resistance of the sensor decreases. As the coolant temperature changes, so does the resistance of the sensor. The gauge is calibrated within the operating range of the sensor and interprets the resistance value to display the coolant temperature.
Beginning with model year 1994, the engine coolant gauge and the Engine Control Module (ECM) temperature sensors were combined into one sensor with 4 terminals. The basic operation remains the same in that their resistance decreases as the coolant temperature increases, however the actual resistance values of the 2 sensor circuits are different. The electrical connector of the 4-wire terminal sensor ( 1 and 2 ) is keyed to prevent improper connection of the sensor's electrical circuit.

Fig. Beginning with model year 1994, the Engine Coolant Temperature Sensors combined the sensors for the ECM and the gauge into one sensor-1997 2.8L V6 sensor shown

Fig. The electrical connector for the combined temperature sensors is keyed to avoid improperly connecting the sensor's wiring-1997 2.8L V6 connector shown

Look for a loose connection to the temperature sender unit on the motor.
If all connections OK, you may need a new temp sender unit.

this is the coolant temp sensor, it sends a signal to the engine ECU
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this is the temp sending unit. it sends a signal to the gauge on the instrument panel.
this is what you need to get to fix your temp gauge.