MAP Pressure: Absolute vs. Gauge

Absolute and gauge pressure

Absolute pressure is measured from vacuum. Gauge pressure is measured from local atmospheric pressure. A psia rating is absolute: it is not the same pressure as boost above atmosphere.

The conversion

Gauge pressure = absolute pressure − local atmospheric pressure. Use the actual atmospheric pressure and matching units when comparing a sensor range with a boost target.

A name is not a calibration

A model name such as “4.0 MAP” does not by itself establish the range, voltage curve or pressure reference. Check the exact part number, sensor supply, signal output and calibration expected by the ECU.

Checklist & example

• At 100 kPa local atmospheric pressure, a 200 kPa MAP reading corresponds to 100 kPa gauge boost.
• Use the actual local atmospheric pressure for conversion, and check the sensor’s absolute-pressure range separately when selecting it.