Corsica L4-2.2L VIN 4 (1995)
Manifold Pressure/Vacuum Sensor: Description and Operation
MAP Sensor
PURPOSE
The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure which results from engine load and speed
changes, and converts them to a voltage output.
OPERATION
A closed throttle on engine coastdown would produce a relatively low MAP voltage output, while a wide open throttle would produce a high
voltage output. Manifold absolute pressure is the OPPOSITE of what you would measure on a vacuum gauge. When manifold pressure is high,
vacuum is low. The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the Powertrain Control
Module (PCM) to automatically adjust to different altitudes. The PCM sends a 5 volt reference signal to the MAP sensor. As manifold pressure
changes, electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the manifold pressure. A high
pressure, low vacuum (high voltage) condition requires more fuel, while a low pressure, high vacuum (low voltage) requires less fuel.
A fault in the MAP sensor circuit should set a Diagnostic Trouble Code (DTC) 33 or DTC 34.
