9-5 Sport Wagon (9600) L4-2.3L Turbo (B235) (2003)
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Manifold Pressure/Vacuum Sensor: Description and Operation
Manifold Absolute Pressure Sensor
Inside the pressure sensor there are two metal-plated ceramic discs mounted close together. The disc situated closest to the pressure connection is thinner
and bends when exposed to pressure. This changes the capacitance between the metal-plated discs depending on the pressure. Integrated in the sensor is
a circuit that converts capacitance to analogue voltage. The pressure sensor is screwed to the intake manifold on the engine after the throttle and is
powered with 5V from control module pin 69 and grounded from control module pin 22.
Depending on the pressure in the intake manifold, the pressure sensor delivers a voltage to control module pin 11.
During rapid load changes, the engine load or calculated air mass/combustion based on the mass air flow sensor value can differ from the actual air mass
being taken into the cylinder during the induction stroke. This is due to the inertia of the large volume of air present in the intake system. The intake
pressure is therefore used during load changes to correct the air mass/combustion used in the basic calculation of the fuel quantity.
The pressure is also used to correct the purge PWM ratio. A greater PWM ratio is required at high intake pressures to obtain the same purge flow.
At normal atmospheric pressure, 100 kPa, the pressure from the sensor is approx 2.1 V.
