Sunfire L4-138 2.3L DOHC VIN D MFI (1995)
Manifold Absolute Pressure (MAP) Sensor: Description and Operation
Manifold Absolute Pressure Sensor
PURPOSE
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load and speed
changes, and converts this to a voltage output. By monitoring the sensor output voltage, the Powertrain Control Module (PCM) knows the
manifold pressure. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires
less fuel.
OPERATION
A closed throttle on engine coastdown would produce a relatively low MAP output, while a wide open throttle would produce a high output. MAP
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 PCM to automatically adjust for different altitudes. The PCM sends a 5
volt reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes.
A high or low voltage fault in the MAP sensor circuit should set a DTC P0107 or DTC P0108. It the MAP sensor sends an intermittent zero
voltage signal to the PCM, a DTC P0106 will set.
