Ive replaced lots on these, It usually is the coolant fan switch. On the thermostat housing there is , depending the model there are 2 temp switches, one controls the temp gauge and the other the cooling fan. . The way to test them is one , its usually the one with the green base. Unplugg the sensor( one closer to the engine) and with a test light plugged to the ground( we are not checking for voltage though, just usuing the low supression ground of the test light) with sumone sitting inside have them turn the key to the on position DONT start the car!!! probe both side of the terminal , keeping it probbed for 3 secs each), with sumone watching the temp gauge in the car 2 things should happen 1: the cooling fan should kick on and off as soon as yu remover the tester frum the plug in , or 2 the coolant needle will start to sweep towards the H side on the gauges in the car. If the temp gauge budges, then repeat this procedure with the outter sensor on the thermostat housing. If after doing the following procedure and 1 or 2 does not happen there is a fault with the PCM. if the gauge moves and after probing the other sensor and still nothing there is a possible fan problem or PCM issue. On some models there is one sensor on the thermostat housing and one located in the cylinder head near the thermostat housing. The sensor with the one wire plug in is the oil pressure sending switch, do not touch it.I have foung the plug in on them break very easilly even when being gentle lol