Riviera V6-231 3.8L VIN L SFI (1991)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
Coolant Temperature Sensor
The coolant sensor is a thermistor (a resistor which varies its resistance value based on temperature) mounted in the engine coolant stream. The coolant
sensor is a two wire component which receives a reference voltage signal from the ECM/PCM. Low coolant temperature produces a high resistance,
while a high temperature produces low resistance. The ECM/PCM supplies a 5.0 volt signal to the coolant sensor through a resistor in the ECM/PCM
and measures the signal voltage output. The voltage will be high when the engine is cold, and the voltage will be low when the engine is hot. By
measuring the voltage, the ECM/PCM calculates the engine coolant temperature. Engine coolant temperature affects most systems the ECM/PCM
controls. ED04 displays engine temperature in degrees centigrade. After engine start-up, the temperature should rise steadily to about 90°C then stabilize
when the thermostat opens. If the engine has not been run for several hours the coolant temperature and MAT temperatures should read close to each
other.
The sensor provides coolant temperature information to the ECM/PCM for fuel enrichment, ignition timing, EGR operation, canister purge control, air
management, idle speed control, and closed loop fuel control. A failure in the coolant sensor circuit should set either a code E014 or code E015.
