900 SE Convertible V6-2489cc 2.5L DOHC EFI (1997)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
The temperature sensor is positioned on the lefthand side of the engine in the pipe between the front and rear cylinder heads. It is of NTC type.
The control module measures the coolant temperature by supplying the sensor with 5 V from pin 74 via an integral 1 kohm resistor. The sensor is
grounded via pin 71 of the control module.
The voltage across the integral resistor in the control module is proportional to the temperature of the coolant.
This voltage is used to determine:
^
the injection time for pre-injection
^
the injection time for cold starting and warming-up enrichment
^
engagement of closed loop
^
idling speed.
^
ignition timing during warm-up and knock control
Should the sensor fail to work or in the event of a break in the circuit (no continuity), the control module will use a default temperature of 70.5°C (159°
F) if the fault occurs while the engine is running. If the engine is started with a defective coolant temperature circuit, the intake air temperature sensor
will take over the function of the coolant temperature sensor when the engine is started, following which the value of the coolant temperature will be
incremented by about 1°C every 10 seconds until a temperature of 70.5°C (159°F) is reached.
