Intake air sensor (688), PSG16
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Intake air sensor (688), PSG16
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Intake air sensor (688)
The sensor is a combined pressure and temperature sensor. It measures the prevailing absolute pressure and temperature in the charge air pipe.
The temperature is used to:
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Together with the boost pressure determine the density of the charge air. The charge air density is used by airmass control to correct the throttle angle.
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Correct the charge air control valve PWM ratio. A higher PWM ratio is required at high temperature to obtain the same air mass/combustion.
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Correct ignition angle. An advanced timing is required at low temperatures.
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Blocking certain diagnostics:
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Blocks certain diagnostics at temperatures lower than -7°C.
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Reactivates certain diagnostics at temperatures higher than +5°C.
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The pressure sensor contains two metal-coated ceramic discs fitted close together. The disc located closest to the pressure connection is thinner and bends when exerted to pressure. The temperature sensor is of NTC type.
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Pin No.
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Signal type
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Description
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1
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Ground
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Connected to ECM pin 46(M)
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2
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Signal, temperature
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Connected to ECM pin 22(M)
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3
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Power supply, 5V
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Connected to ECM pin 39(M)
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4
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Signal, pressure
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Connected to ECM pin 9(M)
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The capacitance between the metal coating on the discs changed depending on the pressure. Integrated in the sensor is a circuit that converts the capacity to an analogue voltage.
Depending on the pressure in the charge air pipe, the pressure sensor will supply a proportional voltage to the control module pin 9(M).
The control module measures the air temperature in the intake manifold by supply the sensor with 5V through a 1.50 kohm resistor from pin 22(M). The voltage across the resistor in the control module is proportional to the intake air temperature.
The mass air control determines the air mass/combustion to be drawn in during the cylinder's intake stroke. The value corresponds to the torque of the engine.
Throttle control adjusts the throttle so that the current air mass/combustion is the same as the one requested. If the air before the throttle is dense, a smaller throttle angle is required than if the air density is lower. The density of the air is therefore calculated by the control module using the boost pressure and intake air temperature.
At normal atmospheric pressure, 100 kPa, the voltage form the sensor is approx. 2.1V.
