Engine coolant temperature sensor
68
The temperature sensor is located in the intake man-
ifold between the intake manifolds of cylinders 2 and
3 and is in contact with the engine coolant. The sen-
sor is of the NTC type.
The engine. control module measures the coolant
temperature by applying 5 V to the sensor from pin
68 via an integral 2. 7 4 kohm resistor. The sensor is
grounded via pin 67 of the control module.
The ECM receives reference ground from the sensor
ground lead to pin 66 to obtain a precise temperature
measurement. The voltage across the resistor in the
ECM is proportional to the coolant temperature.
The voltage is used to determine fuel injection dura-
tion for pre-injection as well as for cold starting and
producing a richer fuel/air mixture during the warm-
ing-up ·period. Activation of closed loop and idling
speed is also dependent on engine coolant tempera-
ture.
In the event of sensor failure or a break in the circuit,
the engine control module will set a default tempera-
ture that is equivalent to the intake air temperature on
starting and then increased by 1 °c (1.8°F) every
15oth engine revolution.
Saab 9000
202
Technical Description 33
I
589
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