A DTC will be set if an abnormal reading occurs, P0116 for sensor performance, P0117 low input or
P0118 for a high input. The coolant temperature sensor temperature reading should closely match the
air charge/manifold temperature reading on a scan tool if the engine has not been run for over an hour.
The sensor circuit can be checked for proper voltage using a voltmeter.
Cooling Fan Switch
Engine Temperature Sensor
Temperature Switch
Fig. Remove the coolant temperature sensor
The coolant temperature gauge sensor is a temperature-variable resistor, or thermistor. As coolant temperature increases, the resistance of the sensor decreases or decreases, depending on the type of sensor.
A1 and A2 platforms use a different type of circuit that A3 vehicles. On A1 and A2 vehicles, the circuit is a "resistance to ground" type. A3 vehicles use a "variable voltage" type, where a voltage is supplied to the sensor. Because of the circuitry design on A3 vehicles, testing of the coolant temperature gauge is limited.
The engine coolant temperature gauge uses a heat sensitive sending unit to transmit an electrical signal to the gauge. The sending unit is a heat sensitive variable resistor that is located on or near to the cylinder head and threads into an engine coolant passage. The sensors are a Negative Temperature Coefficient (NTC) type. As the temperature increases, the electrical resistance of the sensor decreases. As the coolant temperature changes, so does the resistance of the sensor. The gauge is calibrated within the operating range of the sensor and interprets the resistance value to display the coolant temperature.
Beginning with model year 1994, the engine coolant gauge and the Engine Control Module (ECM) temperature sensors were combined into one sensor with 4 terminals. The basic operation remains the same in that their resistance decreases as the coolant temperature increases, however the actual resistance values of the 2 sensor circuits are different. The electrical connector of the 4-wire terminal sensor ( 1 and 2 ) is keyed to prevent improper connection of the sensor's electrical circuit.
Fig. Beginning with model year 1994, the Engine Coolant Temperature Sensors combined the sensors for the ECM and the gauge into one sensor-1997 2.8L V6 sensor shown
Fig. The electrical connector for the combined temperature sensors is keyed to avoid improperly connecting the sensor's wiring-1997 2.8L V6 connector shown
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