Grand AM L4-144 2.4L DOHC VIN T SFI (1997)
Purge Flow Sensor: Description and Operation
Description
The fuel tank vapor pressure sensor is a 3 wire strain gauge similar to the Manifold Absolute Pressure (MAP) sensor. It is used to measure the difference
between the air pressure (or vacuum) in the fuel tank and the outside air pressure. However, this sensor has very different electrical characteristics due to
its pressure differential design.
Operation
The PCM supplies a 5 volt reference and a ground to the sensor. The sensor sends a voltage signal between 0.1 and 4.9 volts back to the PCM. When the
air pressure in the fuel tank is equal to the outside air pressure, as when the fuel cap is removed, the output voltage of the sensor will be from 1.3 to 1.7
volts. When the air pressure in the tank is 4.5 inches H2O (1.25 kPa) greater than atmospheric pressure, the sensor output voltage should measure 0.5 +/-
0.2 volts. At 14 inches H2O (3.75 kPa) below atmospheric pressure, the sensor output voltage should be 4.5 volts +/- 0.2 volts.
