Prizm L4-1800cc 1.8L DOHC (1993)
Manifold Pressure/Vacuum Sensor: Description and Operation
MAP Sensor
MAP Sensor Output Characteristic
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load and speed changes.
The PCM converts this to a voltage output.
The PCM sends a 5.0 volts reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By
monitoring the sensor output voltage, the 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.
A closed throttle on engine coast down would produce a relatively low MAP output, while a wide-open throttle would produce a high output. MAP
sensor pressure is the opposite of what would be measured on a vacuum gauge. When manifold pressure is high, vacuum is low.
The MAP sensor is also used to measure barometric pressure under certain conitions, which allows the PCM to automatically adjust for different
altitudes.
A failure in the MAP sensor circuit should set a Code 31.
