Intake air sensor (688), E39
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Intake air sensor (688), E39
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Mounted on charge air pipe.
Intake air sensor (688), E39
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The intake air sensor (688), E39, is a combined pressure and temperature sensor. It measures the prevailing absolute pressure with pressure sensor (603) and the temperature in the charge air pipe with temperature sensor (407). The intake air sensor (688), E39, is connected to ECM, E39 (590).
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 body (603) contains two metal plated ceramic discs mounted in close proximity. The disc located closest to the pressure connection is thinner and bends when subjected to pressure. By this means, capacitance between the metal plating of the discs is changed based on the pressure. A circuit integrated in the pressure sensor body 603 converts the capacitance to an analogue output voltage.
The pressure sensor temperature sensor (407), which is an NTC type, contains a circuit that delivers an output voltage that corresponds to the temperature.
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688 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 20(A).
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2
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Temperature signal
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Connected to ECM pin 13(A).
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3
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Power supply, 5 V
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Connected to ECM pin 5(A).
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4
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Pressure signal
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Connected to ECM pin 4(A).
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Pressure measurement
Based on the pressure in the charge air pipe, the pressure sensor (603) yields a proportional voltage to the ECM, E39 (590), pin 4(A). At normal atmospheric pressure, 100 kPa, the output voltage is approx. 2.1 V.
Temperature measurement
The temperature sensor (407) measures the air temperature in the intake manifold. The output voltage to ECM, E39 (590) pin 13(A) is proportional to the temperature of the intake air.
Throttle control
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 ECM, E39 (590), using the boost pressure and intake air temperature.
