<Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (December 2013) (Learn how and when to remove this template message) </Td> </Tr> <P> The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an internal combustion engine's electronic control system . </P> <P> Engines that use a MAP sensor are typically fuel injected . 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 (see stoichiometry) and influence the advance or retard of ignition timing . A fuel - injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow . A typical naturally aspirated engine configuration employs one or the other, whereas forced induction engines typically use both; a MAF sensor on the intake tract pre-turbo and a MAP sensor on the charge pipe leading to the throttle body . </P> <P> MAP sensor data can be converted to air mass data using the speed - density method . Engine speed (RPM) and air temperature are also necessary to complete the speed - density calculation . The MAP sensor can also be used in OBD II (on - board diagnostics) applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines . </P>

What is the purpose of the map sensor
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