Intake air sensor (688), T8
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Intake air sensor (688), T8
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Intake air sensor (688)
The sensor is a combined pressure and temperature sensor. The sensor measures the current absolute pressure and temperature in the charge air pipe.
Temperature is used to:
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Together with boost pressure determine charge air density. Charge air density is used by airmass control to correct the throttle angle.
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Correct the charge air control valve's PWM ratio. At high temperatures, a higher PWM ratio is required to maintain the same airmass/combustion.
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Correct ignition angle. At low temperatures, earlier ignition is required.
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Blocking of certain diagnostics:
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Blocks certain diagnostics at temperatures below -7°C.
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Reactivates certain diagnostics at temperatures greater than +5°C.
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The pressure sensor 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. 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 43(B).
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2
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Temperature signal
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Connected to ECM pin 10(B).
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3
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Power supply, 5 V
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Connected to ECM pin 45(B).
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4
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Pressure signal
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Connected to ECM pin 24(B).
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Sensor capacitance between the metal plating of the discs is changed based on the pressure. A circuit integrated in the sensor converts the capacitance to an analogue voltage.
Based on the pressure in the charge air pipe, the pressure sensor yields a proportional voltage to control module pin 24(B).
The control module measures air temperature in the induction pipe by supplying the sensor 5 V through a 1.50 kOhm resistor integrated in the control module from pin 10(B). Voltage across the resistor in the control module is proportional to the intake air temperature.
Airmass control determines which airmass/combustion is to be sucked in during the cylinder's intake stroke. The value corresponds to engine torque.
Throttle control sets the throttle so that the actual airmass/combustion matches that which is requested. If air density before the throttle is high, a smaller throttle angle is required than if the air density is low. Air density is therefore calculated by the control module using boost pressure and intake air temperature.
At normal atmospheric pressure, 100 kPa, voltage from the sensor is approx. 2.1 V.
