Manifold Absolute Pressure sensor (MAP sensor) is one type of the pressure sensors used in an internal combustion engine’s electronic control system (ECU). Engines that use a MAP sensor are typically fuel injected. MAP sensor helps to measure engine load so that the engine ECU computer may alter spark timing and the air-fuel mixture to improve vehicle performance (fuel economy, acceleration) and emissions. MAP sensor can also be used in OBD II (on-board diagnostics) applications to test the EGR (exhaust gas recirculation) valve for functionality.

The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine’s electronic control unit (ECU). The data is used to calculate air density and determine the engine’s air mass flow rate, which in turn determines the required fuel metering for optimum combustion. A fuel-injected engine may alternately use a MAF (mass air flow) sensor to detect the intake airflow.

A MAP (Manifold Absolute Pressure) Sensor is a micromechanical sensor that measures the absolute pressure in the intake manifold and compares it with a reference vacuum, not with the ambient pressure. This information is used by the engine computer to monitor engine load (vacuum drops when the engine is under load or at wide open throttle). When the engine is under load, the computer may alter spark timing and the fuel mixture to improve vehicle performance (fuel economy, acceleration) and emissions.

A bad MAP sensor does not generally prevent a vehicle’s motor from operating. But a bad MAP sensor can affect the vehicle performance (fuel economy, acceleration) and emissions that have an impact on the drivability of a vehicle. This can be attributed to the loss of horsepower that results when the air-fuel mixture is not properly balanced.

Some of Manifold Absolute Pressure sensor (MAP sensor) problems are not the fault of the sensor itself. If the vacuum hose that connects the MAP sensor to the intake manifold is loose, leaking or plugged, the sensor cannot produce an accurate signal. Also, if there is a problem within the engine itself that causes intake vacuum to be lower than normal (such as a vacuum leak, EGR valve that is stuck open or leaky PCV hose), the MAP sensor’s readings may be lower than normal.