MaP sensor - wikipedia MaP sensor The examples and descriptions in this article apply strictly to four - stroke cycle gasoline engines. Other engine types such as diesel, or two - stroke cycle can differ in the exact implementation, but the general ideas still apply. 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 ) The manifold absolute pressure sensor ( MAP sensor ) is one of the sensors used in an internal combustion engine 's electronic control system. 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. 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. Contents 1 Example 2 Vacuum comparison 3 EGR testing 3.1 Common confusion with boost sensors and gauges 4 References 5 External links Example The following example assumes the same engine speed and air temperature. Condition 1 : An engine operating at wide open throttle ( WOT ) on top of a very high mountain has a manifold pressure of about 50 kPa ( essentially equal to the barometer at that high altitude ). Condition 2 : The same engine at sea level will achieve 50 kPa ( 7.25 psi, 14.7 inHG ) of manifold pressure at less than WOT due to the higher barometric pressure. The engine requires the same mass of fuel in both conditions because the mass of air entering the cylinders is the same. If the throttle is opened all the way in condition 2, the manifold absolute pressure will increase from 50 kPa to nearly 100 kPa ( 14.5 psi, 29.53 inHG ), about equal to the local barometer, which in condition 2 is sea level. The higher absolute pressure in the intake manifold increases the air 's density, and in turn more fuel can be burned resulting in higher output. Another example is varying rpm and engine loads - Where an engine may have 60kPa of manifold pressure at 1800 rpm in an unloaded condition, introducing load with a further throttle opening will change the final manifold pressure to 100kPa, engine will still be at 1800 rpm but its loading will require a different spark and fueling delivery. Vacuum comparison Engine vacuum is the difference between the pressures in the intake manifold and ambient atmospheric pressure. Engine vacuum is a `` gauge '' pressure, since gauges by nature measure a pressure difference, not an absolute pressure. The engine fundamentally responds to air mass, not vacuum, and absolute pressure is necessary to calculate mass. The mass of air entering the engine is directly proportional to the air density, which is proportional to the absolute pressure, and inversely proportional to the absolute temperature. Note : Carburetors are largely dependent on air volume flow and vacuum, and neither directly infers mass. Consequently, carburetors are precise, but not accurate fuel metering devices. Carburetors were replaced by more accurate fuel metering methods, such as fuel injection in combination with an air mass flow sensor ( MAF ). EGR testing With OBD II standards, vehicle manufacturers were required to test the exhaust gas recirculation ( EGR ) valve for functionality during driving. Some manufacturers use the MaP sensor to accomplish this. In these vehicles, they have a MAF sensor for their primary load sensor. The MaP sensor is then used for rationality checks and to test the EGR valve. The way they do this is during a deceleration of the vehicle when there is low absolute pressure in the intake manifold ( i.e., a high vacuum present in the intake manifold relative to the outside air ) the powertrain control module ( PCM ) will open the EGR valve and then monitor the MaP sensor 's values. If the EGR is functioning properly, the manifold absolute pressure will increase as exhaust gases enter. Common confusion with boost sensors and gauges MAP sensors measure absolute pressure. Boost sensors or gauges measure the amount of pressure above a set absolute pressure. That set absolute pressure is usually 100 kPa. This is commonly referred to as gauge pressure. Boost pressure is relative to absolute pressure - as one increases or decreases, so does the other. It is a one - to - one relationship with an offset of - 100 kPa for boost pressure. Thus a MaP sensor will always read 100 kPa more than a boost sensor measuring the same conditions. A MaP sensor will never display a negative reading because it is measuring absolute pressure, where zero is the total absence of pressure. Vacuum is measured as a negative pressure relative to normal atmospheric pressure. Vacuum - Boost sensors can display negative readings, indicating vacuum or suction ( a condition of lower pressure than the surrounding atmosphere ). In forced induction engines ( supercharged or turbocharged ), a negative boost reading indicates that the engine is drawing air faster than it is being supplied, creating suction. The suction is caused by throttling in spark ignition engines and is not present in diesel engines. This is often called vacuum pressure when referring to internal combustion engines. In short, most boost sensors will read 100 kPa less than a MaP sensor reads. One can convert boost to MaP by adding 100 kPa. One can convert from MaP to boost by subtracting 100 kPa. References External links MaP sensor Automotive engine Part of the Automobile series Basic terminology Bore Compression ratio Crank Cylinder Dead centre Diesel engine Dry sump Engine balance Engine configuration Engine displacement Engine knocking Firing order Hydrolock Petrol engine Power band Redline Spark - ignition engine Stroke Stroke ratio Wet sump Main components Connecting rod Crankcase Crankpin Crankshaft Crossplane Cylinder bank Cylinder block Cylinder head ( crossflow, reverse - flow ) Flywheel Head gasket Hypereutectic piston Main bearing Piston Piston ring Starter ring gear Sump Valvetrain Cam Cam follower Camshaft Desmodromic valve Hydraulic tappet Multi-valve Overhead camshaft Overhead valve Pneumatic valve springs Poppet valve Pushrod Rocker arm Sleeve valve Tappet Timing belt Timing mark Valve float Variable valve timing Aspiration Air filter Blowoff valve Boost controller Butterfly valve Centrifugal - type supercharger Cold air intake Dump valve Electronic throttle control Forced induction Inlet manifold Intake Intercooler Manifold vacuum Naturally aspirated engine Ram - air intake Scroll - type supercharger Short ram air intake Supercharger Throttle Throttle body Turbocharger Twin - turbo Variable - geometry turbocharger Variable - length intake manifold Warm air intake Fuel system Carburetor Common rail Direct injection Fuel filter Fuel injection Fuel pump Fuel tank Gasoline direct injection Indirect injection Injection pump Lean - burn Stratified charge engine Turbo fuel stratified injection Unit injector Ignition Contact breaker Magneto Distributor Electrical ballast High tension leads Ignition coil Spark plug Wasted spark Electrics and engine management Air -- fuel ratio meter Alternator Automatic Performance Control Car battery ( lead -- acid battery ) Crankshaft position sensor Dynamo Drive by wire Electronic control unit Engine control unit Engine coolant temperature sensor Glow plug Idle air control actuator MAP sensor Mass flow sensor Oxygen sensor Starter motor Throttle position sensor Exhaust system Automobile emissions control Catalytic converter Diesel particulate filter Exhaust manifold Glasspack Muffler Engine cooling Air cooling Antifreeze ( ethylene glycol ) Core plug Electric fan Fan belt Radiator Thermostat Water cooling Viscous fan ( fan clutch ) Other components Balance shaft Block heater Combustion chamber Cylinder head porting Gasket Motor oil Oil filter Oil pump Oil sludge PCV valve Seal Synthetic oil Underdrive pulleys Portal Sensors Acoustic, sound, vibration Geophone Hydrophone Microphone Seismometer Automotive, transportation Air -- fuel ratio meter Blind spot monitor Crankshaft position sensor Curb feeler Defect detector Engine coolant temperature sensor Hall effect sensor MAP sensor Mass flow sensor Omniview technology Oxygen sensor Parking sensors Radar gun Speed sensor Speedometer Throttle position sensor Tire - pressure monitoring system Torque sensor Transmission fluid temperature sensor Turbine speed sensor Variable reluctance sensor Vehicle speed sensor Water sensor Wheel speed sensor Chemical Breathalyzer Carbon dioxide sensor Carbon monoxide detector Catalytic bead sensor Chemical field - effect transistor Electrochemical gas sensor Electrolyte -- insulator -- semiconductor sensor Electronic nose Fluorescent chloride sensors Holographic sensor Hydrocarbon dew point analyzer Hydrogen sensor Hydrogen sulfide sensor Infrared point sensor Ion selective electrode Microwave chemistry sensor Nitrogen oxide sensor Nondispersive infrared sensor Olfactometer Optode Oxygen sensor Pellistor pH glass electrode Potentiometric sensor Redox electrode Smoke detector Zinc oxide nanorod sensor Electric, magnetic, radio Current sensor Electroscope Galvanometer Hall effect sensor Hall probe Magnetic anomaly detector Magnetometer MEMS magnetic field sensor Metal detector Planar Hall sensor Radio direction finder Test light Environment, weather, moisture Actinometer Bedwetting alarm Ceilometer Dew warning Electrochemical gas sensor Fish counter Frequency domain sensor Gas detector Hook gauge evaporimeter Humistor Hygrometer Leaf sensor Psychrometer Pyranometer Pyrgeometer Rain gauge Rain sensor SNOTEL Snow gauge Soil moisture sensor Stream gauge Tide gauge Weather radar Flow, fluid velocity Air flow meter Anemometer Flow sensor Gas meter Mass flow sensor Water metering Ionising radiation, subatomic particles Bubble chamber Cloud chamber Geiger -- Müller tube Geiger counter Ionization chamber Neutron detection Particle detector Proportional counter Scintillation counter Semiconductor detector Scintillator Thermoluminescent dosimeter Wire chamber Navigation instruments Airspeed indicator Machmeter Altimeter Attitude indicator Depth gauge Fluxgate compass Gyroscope Inertial navigation system Inertial reference unit Magnetic compass MHD sensor Ring laser gyroscope Turn coordinator Variometer Vibrating structure gyroscope Yaw - rate sensor Position, angle, displacement Accelerometer Angular rate sensor Auxanometer Capacitive displacement sensor Capacitive sensing Gravimeter Inclinometer Integrated circuit piezoelectric sensor Laser rangefinder Laser surface velocimeter Lidar Linear encoder Linear variable differential transformer Liquid capacitive inclinometers Odometer Photoelectric sensor Piezoelectric accelerometer Position sensor Rotary encoder Rotary variable differential transformer Selsyn Sudden Motion Sensor Tachometer Tilt sensor Ultrasonic thickness gauge Variable reluctance sensor Velocity receiver Optical, light, imaging Active pixel sensor Angle -- sensitive pixel Back - illuminated sensor Charge - coupled device Contact image sensor Electro - optical sensor Flame detector Infrared Kinetic inductance detector LED as light sensor Light - addressable potentiometric sensor Nichols radiometer Optical fiber Photodetector Photodiode Photoelectric sensor Photoionization detector Photomultiplier Photoresistor Photoswitch Phototransistor Phototube Position sensitive device Scintillometer Shack -- Hartmann wavefront sensor Single - photon avalanche diode Superconducting nanowire single - photon detector Transition edge sensor Tristimulus colorimeter Visible - light photon counter Wavefront sensor Pressure Barograph Barometer Boost gauge Bourdon gauge Hot - filament ionization gauge Ionization gauge McLeod gauge Oscillating U-tube Permanent Downhole Gauge Piezometer Pirani gauge Pressure gauge Pressure sensor Tactile sensor Time pressure gauge Force, density, level Bhangmeter Force gauge Hydrometer Level sensor Load cell Magnetic level gauge Nuclear density gauge Piezoelectric sensor Strain gauge Torque sensor Viscometer Thermal, heat, temperature Bimetallic strip Bolometer Calorimeter Exhaust gas temperature gauge Flame detection Gardon gauge Golay cell Heat flux sensor Infrared thermometer Microbolometer Microwave radiometer Net radiometer Quartz thermometer Resistance thermometer Silicon bandgap temperature sensor Special sensor microwave / imager Thermistor Thermocouple Thermometer Proximity, presence Alarm sensor Doppler radar Motion detector Occupancy sensor Passive infrared sensor Proximity sensor Reed switch Stud finder Touch switch Triangulation sensor Wired glove Sensor technology Active pixel sensor Back - illuminated sensor Biochip Biosensor Capacitance probe Carbon paste electrode Catadioptric sensor Digital sensors Displacement receiver Electromechanical film Electro - optical sensor Fabry -- Pérot interferometer Fisheries acoustics Image sensor Image sensor format Inductive sensor Intelligent sensor Lab - on - a-chip Leaf sensor Machine vision Microelectromechanical systems Photoelasticity Quantum sensor Radar Ground - penetrating radar Synthetic aperture radar Radar tracker Sensor array Sensor fusion Sensor grid Sensor node Soft sensor Sonar Staring array Transducer Ultrasonic sensor Video sensor technology Visual sensor network Wheatstone bridge Wireless sensor network Related List of sensors Retrieved from `` https://en.wikipedia.org/w/index.php?title=MAP_sensor&oldid=844043826 '' Categories : Engine components Engine fuel system technology Engine sensors Engines Hidden categories : Articles lacking in - text citations from December 2013 All articles lacking in - text citations Talk Contents About Wikipedia Deutsch Ελληνικά Bahasa Indonesia 日本 語 Norsk Svenska Edit links This page was last edited on 2 June 2018, at 06 : 34 ( UTC ). 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Question: what does a map sensor do for a car
Answer: provides instantaneous manifold pressure information to the engine's electronic control unit (ECU)