Century V6-3100 3.1L VIN M SFI (1998)
Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection
Following is a short description of how the Engine Coolant Temperature (ECT) Sensor can be diagnosed by using a scan tool. The scan tool can also be
used to compare the values for a normal running engine with the engine you are diagnosing.
DESCRIPTION
The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream.
Low coolant temperature produces a high resistance (100,000) ohm at -40°C/-40°F) while high temperature causes low resistance (70°C at 130°C/266
°F).
OPERATION
The PCM supplies a 5 volt signal to the engine coolant temperature sensor through a resistor in the PCM and measures the voltage. The voltage will
be high when the engine is cold, and low when the engine is hot. By measuring the voltage, the PCM calculates the engine coolant temperature.
Engine coolant temperature affects most systems the PCM controls.
DIAGNOSIS
The scan tool displays engine coolant temperature in degrees. After engine start-up, the temperature should rise steadily to about 90°C (194°F) then
stabilize when thermostat opens. If the engine has not been run for several hours (overnight), the engine coolant temperature and intake air
temperature displays should be close to each other. A hard fault in the engine coolant sensor circuit should set DTC P0117 or DTC P0118, an
intermittent fault should set a DTC P1114 or P1115. Refer to System DIagnosis / Diagnostic Tables / Diagnostic Trouble Code Tables. See: Testing
and Inspection
The DTC Diagnostic Aids also contains a chart to check for sensor resistance values relative to temperature. Refer to Specifications / Temperature
vs Resistance. The ECT sensor also contains another circuit which is used to operate the engine coolant temperature gauge located in the instrument
panel.
