K 1500 Truck 4WD V8-4.8L VIN V (1999)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature) mounted in the left cylinder head. Low
coolant temperature produces a high resistance (100,000 ohms at -38°C/-39°F) while high temperature causes low resistance (70 ohms at 130°C/266°
F).
The PCM supplies a 5.0 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. The voltage will be low when the engine is hot. The PCM calculates the engine coolant temperature by measuring the
voltage. The engine coolant temperature affects most systems the PCM controls.
The scan tool displays engine coolant temperature in degrees. When the engine starts the engine coolant temperature should rise steadily to about 90°C
(194°F) then stabilize when thermostat opens. The engine coolant temperature and intake air temperature should be close to each other if the engine has
not been run for several hours (overnight). The following DTCs set when the PCM detects a malfunction in the ECT sensor circuit:
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DTC P0117 ECT Sensor Circuit Low Voltage.
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DTC P0118 ECT Sensor Circuit High Voltage.
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DTC P0125 Excessive Time to Closed Loop.
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DTC P1114 ECT Sensor CKT Intermittent Low Voltage.
^
DTC P1115 ECT Sensor CKT Intermittent High Voltage.
Specifications contains a table to check for sensor resistance values relative to temperature.
