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Manifold Air Pressure Sensor (MAP)

Updated: Jan 9

The manifold absolute pressure (MAP) sensor is a device used by the engine control unit (ECU) to calculate the fuel injection needed for the optimal air-fuel ratio in an internal combustion engine.


MAP sensors are also commonly referred to as:

  • Manifold absolute pressure sensor

  • Engine load sensor

  • Pressure sensor

  • Boost sensor


The MAP sensor continually monitors intake manifold pressure data and is typically used in fuel-injected engines. It is also commonly used in turbocharged and forced induction engines, along with a mass airflow (MAF) sensor.


In addition to its role in fuel injection, the MAP sensor helps the ECU determine when ignition should occur under various engine load conditions.


If the MAP sensor is not functioning properly, the ECU will not be able to optimise fuel injection, which can affect engine performance and cause accelerated wear.

 

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Location & Appearance of the MAP Sensor

A manifold absolute pressure (MAP) sensor is a small electronic device that is typically located on or near the throttle body on the intake manifold of an internal combustion engine, or on the intake tract before the turbo in a turbocharged engine.


A manifold air pressure sensor outlined with a red circle showing its typical location and appearance
MAP sensor outlined with a red circle

It typically has a cylindrical shape sensor with a rectangular shaped body, it's usually is made of plastic.


The MAP sensor may have a hose or tube connected to it, which carries the vacuum or pressure from the intake manifold. It may also have electrical connectors and wiring, which allow it to send data to the engine control unit (ECU).


The image below shows what MAP sensors usually look like.


examples of MAP sensors showing the typical appearance of a MAP sensor

The MAP sensor may be mounted to the engine using bolts or clips. It is usually small enough to fit in the palm of your hand and may have a label or markings indicating its manufacturer and model.


How Manifold Air Pressure Sensors Work

It consists of a sealed chamber with a calibrated vacuum or controlled pressure and a flexible silicon wafer known as a "chip" that separates the vacuum from the sensor and the vacuum from the intake manifold.


When the key is turned on, the MAP sensor acts as a barometric pressure sensor, sending a signal to the ECU that can be used to calculate air density.


As the engine runs, the intake manifold pressure drops, creating a vacuum that is applied to the MAP sensor.


When the throttle / accelerator pedal is pressed, the pressure in the intake manifold rises, reducing the vacuum.


This causes the chip inside the MAP sensor to stretch into the sealed chamber, changing the voltage resistance and signaling the ECU to inject more fuel into the engine.


When the accelerator pedal is released, the chip returns to its idle position as the pressure in the intake manifold decreases.


To determine the engine's air mass flow rate for the ideal air-fuel ratio, the ECU combines readings from the following sensors.


  • Manifold air pressure (MAP) sensor

  • Intake air temperature (IAT) sensor

  • Engine coolant temperature (ECT) sensor

  • Barometric pressure sensor

  • Crankshaft position (CKP) sensor


Other sensors may also be used to more accurately determine or adjust the air-fuel ratio, such as the mass air flow (MAF) sensor.


Causes of MAP Sensor Failure

The Manifold Air Pressure (MAP) sensor is an electronic device that is used to measure changes in air pressure within the engine. However, like other electronic sensors, it can be susceptible to contamination, which can cause it to malfunction.


  • Hose failure: If the MAP sensor is connected to the engine via a hose, this hose may become clogged or leak, preventing the sensor from accurately measuring pressure changes.

  • Vibrations: Excessive vibrations from driving in certain conditions may loosen the connections of the MAP sensor, causing it to fail.

  • Heat: Electrical connectors that are located close to the engine may become overheated and melt or shatter, which can also lead to sensor failure.

  • Corrosion and age: Over time, corrosion and age-related deterioration may also cause the MAP sensor to fail. If the MAP sensor fails, it should be replaced to avoid further engine damage.


Signs of a Failing MAP Sensor

To diagnose a MAP sensor issue, a mechanic will typically use a diagnostic tool to check for fault codes and perform a visual inspection of the sensor and related components.


The manifold air pressure sensor helps to regulate the air-fuel ratio and prevent engine knock, which can cause damage to the internal engine components such as pistons, rods, and bearings.


There are several signs that may indicate a failure of the MAP sensor. These include a rich air-fuel ratio, which can cause a rough idle, poor fuel economy, reduced performance, and a strong smell of fuel.