That is one of many possible causes.
(based on a 96 civic LX) I believe the engine coolant temperature sensor is located on the side of the engine (opposite of the camshaft). If you need more details, I would recommend you to download the service manual on www.manualnguide.com
Coolant Temperature Sensor
One sensor would be for your engine temperature gauge and the other sensor for the OBD II engine management system
This sensor is located on the front of the engine. I've had to replace this one before. It's a pain to get to because in order to access the sensor, you have to perform the same steps as you would to change the timing belt. If you look at the front of the engine, just under and to the vehicle's right of the distributor, you should see a wire leading to the sensor. You may or may not see the sensor itself because it's so badly buried. According to the Nissan Service Manual, the sensor, located on the front side of the driver's side cylinder head, detects cylinder head temperature depending on engine coolant temperature. The electric resistance of this sensor decreases in response to temprature rise. If the ECCS detects that this sensor is bad, it will set a Code No. 13 and set the Check Engine Light. My VG30 is in a 1989 hardbody.
Could be a wiring issue or a completely different problem.
Most vehicles use a temperature sensor and gauge that monitor the engine's coolant temperature. The gauge can either reflect the actual engine temperature (with a needle or a digital reading), or it could display a generalized temperature that informs the operator when the engine is at operating temperature or is dangerously hot. Many older vehicles (made before 1980) also used an engine block temperature sensor. The block sensor was usually impeded in the block and connected a warning light that illuminated when temperatures exceeded a certain amount. Most passenger vehicles did not use a gauge with this type of sensor. Some vehicles, especially those used for commercial and industrial purposes, use an oil temperature sensor. It works very much the same as a coolant sensor and can be placed in the engine, transmission, or both depending on the need. It would be more common for a warning light to be connected to this type of sensor, but there are aftermarket gauges that reflect accurate oil temperature readings.
We have no temperature gauge in our car. Didn't come equipped with one. It probably has a warning light that would illuminate if the engine was getting to hot.
The first thing that I would check is the wiring and the temp sensor @ the engine. Sorry but I do not know where the sensor is located on the engine. Usually they are not too hard to locate. i would replace temperature sender usual located near front of engine near thermostat housing
Engine is overheating, faulty gauge, faulty temp sensor......
Why would the temperature gauge indicate an overheated condition when the engine is not hot. It could be the gauge in the instrument panel. Unlikey however. More likely it is a bad coolant temperature sensor or the wiring from the sensor back to the instrument panel. Inspect the wiring and replace the coolant sensor. The sensor is not too expensive.
P0128: Engine Coolant Temperature is below the Thermostat Regulating Temperature Basically the Computer sees that the engine is running too cold. It could be that the thermostat is stuck open and the engine is actually too cold. Or it could be a bad temperature sensor, wiring to the sensor, or the PCM (computer) has a problem and is making a mistake. I would probably replace the thermostat and ECT (Engine Coolant Temp) Sensor first because both are inexpensive and relatively easy to change.
Check the temperature sensor.