V70 XC AWD L5-2.4L Turbo VIN 56 B5254T (1998)
Barometric Pressure Sensor: Description and Operation
ATMOSPHERIC PRESSURE SENSOR
BA. Atmospheric Pressure Sensor
The Atmospheric Pressure Sensor supplies the Engine Control Module (ECM) with a signal describing air pressure. It provides the engine control
module (ECM) with the car's height above sea level.
Atmospheric pressure sensor acts on the control of:
Boost pressure at high altitude
Injection time when starting at high altitude.
At heights above 2,400 meters the following are disabled:
Pulsed Secondary Air Injection System (PAIR) diagnostic
Mass Air Flow (MAF) Sensor, faulty signal.
The atmospheric pressure sensor contains a piezoelectric crystal in the shape of a diaphragm. One side of this diaphragm is subject to atmospheric
pressure, to other side is acted on by a contained gas. The deformation of the piezo-electric diaphragm, and therefore its resistance is proportional
to air pressure.
The voltage across the sensor is a function of air pressure and, therefore, of sensor resistance.
Voltage can vary between 0 Volts and Volts.
The sensor is supplied with a stabilized voltage of 5 Volts from the engine control module (ECM).
If the signal from the atmospheric pressure sensor is faulty or missing the engine control module (ECM) adopts a substitute value.
The atmospheric pressure sensor is located by the right hood catch.