Neon L4-2.0L SOHC (1995)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
Engine Coolant Temperature Sensor Description
NAME OF CODE:
Closed Loop Temp Not Reached
WHEN MONITORED:
After engine is started, for ten minutes.
SET CONDITION:
The engine temperature does not go above 60° by 10 minutes after the engine is started.
THEORY OF OPERATION:
The engine coolant temperature (ECT) sensor is a negative temperature coefficient (NTC) thermistor-type sensor (resistance varies inversely with
temperature). This means at cold temperatures its resistance is high so the voltage signal will be high. As coolant temperature increases, resistance
decreases and the voltage will be low. This allows the sensor to provide an analog voltage signal (0 to 5-volt) to Powertrain Control Module
(PCM) cavity 28.
To make the sensor more accurate at cold and hot temperatures, the 5-volt signal passes through a 10,000 ohm resistor or through a 1,000 ohm
resistor connected in parallel with the 10,000 ohm resistor, which has a calculated resistance value of 909 ohms. If the engine is cold (below 125°
F), the 5-volt supply to the engine coolant temperature sensor is fed only through the 10,000 ohm resistor inside the PCM. If the engine is warm
(above 125° F), the 5-volt supply to the engine coolant temperature sensor is fed through both resistors.
POSSIBLE CAUSES:
-
Thermostat failure
-
ECT failure
-
Faulty connections
-
Extremely cold ambient temperature
-
PCM failure
