Manifold absolute pressure sensor (MAP)

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By Reinier (Contact Me)
Last Updated 2021-09-06
Automobile Repair Shop Owner

What Does the Manifold absolute pressure sensor (MAP) Do?

The Manifold Absolute Pressure (MAP) sensor supplies the PCM (Powertrain Control Module) with input data on the level of air pressure in the intake manifold in real-time. This information is required to calculate appropriate fuel delivery and ignition timing strategies in variable environmental conditions, with the most notable variables being ambient temperature, humidity, and elevation above sea level, all of which affect air density- and all of which could affect the operation of the engine in various ways unless they are taken into account by the MAP sensor.

Why is the Manifold absolute pressure sensor (MAP) Needed?

As stated above, the MAP sensor measures the difference between atmospheric pressure and the actual pressure in the intake manifold. However, pressure in this context depends on the mass of air that is present in the manifold. Thus, since the pressure in the intake manifold is, or should be, approximately proportional to the volume of the air the engine requires to work during one complete engine cycle, the PCM (Powertrain Control Module) needs to “know” how much air is available in the intake manifold to calculate suitable ignition timing and fuel delivery strategies.

Put differently, this means that the MAP sensor measures the pressure of the air in the intake manifold as a function of the air’s density, which is in its turn, a function not only of elevation above sea level but also of the intake air’s temperature and moisture content.

Therefore, in practice, MAP sensors usually work in conjunction with sensors that measure the barometric pressure and ambient temperature, since cold air is always denser than hot air; moisture-laden air is always denser than dry air, and air at high altitudes is always less dense than air at lower altitudes.

So, while a MAP sensor cannot compensate for environmental factors, all the information from the MAP sensor and other sensors that relate to air pressure is combined to provide the PCM with an absolute intake manifold pressure value. This value forms the basis upon which the PCM calculates appropriate fuel delivery, ignition timing, and variable valve/camshaft timing settings to ensure stable and complete combustion under all environmental and engine operating conditions.

Note, though, that if an engine without forced induction* operates with a large throttle opening, the pressure in the intake manifold can never exceed atmospheric pressure. This is because as the engine “sucks” air out of the manifold, atmospheric pressure forces air into the manifold, but at a slightly lower rate at which the engine sucks the air out of the manifold per intake stroke.

*On engines with forced induction, the pressure inside the intake manifold can, and often does, exceed atmospheric pressure by a significant margin.

At first glance, this would eventually cause the engine to suck all the air out of the manifold, which would create a negative pressure. However, the air in the manifold flows into the engine in pulses, since only one cylinder is drawing air out of the manifold at a time. This creates oscillating pressure waves within the manifold plenum, which helps to maintain a positive pressure in the intake manifold that is always below atmospheric pressure during steady cruising conditions on engines without forced induction.

If, however, the engine runs at high speed and the drive suddenly closes the throttle, the air moving into the manifold at high speed causes a sudden, and severe increase in the intake manifold. If either, or both the ignition timing and fuel delivery remain at current settings, this could cause severe misfires. To prevent this, the MAP sensor relays the sudden pressure increase to the PCM, which then adapts both strategies to maintain proper combustion under the changing conditions.

As a practical matter, an engine cannot operate without input data on the volume of air that is available in the intake manifold, because the PCM cannot calculate fuel delivery and ignition timing strategies without this information. However, on most applications, the PCM will revert to a default strategy when the MAP sensor fails, while on other applications, the barometric pressure sensor will assume some of the functions of the MAP sensor to prevent the MAP sensor failure from immobilizing the vehicle.

How Does the Manifold absolute pressure sensor (MAP) Work?

In all designs, the MAP sensor contains a semi-conductor (mostly some form of piezoelectric crystal or wafer) that responds to changes in pressure. In practice, these crystals or wafers conduct an electrical current that is supplied by the PCM: when the pressure on the crystal or wafer changes, the electrical conductivity of the piezoelectric element changes, so depending on the direction of change, the crystal or wafer will conduct more or less of the supplied current.

The PCM interprets the changes in current flowing back to it as changes in air pressure, and it uses the changes in pressure to adapt fuel delivery and ignition timing strategies continually to maintain proper combustion, and by extension, maximum engine performance under all operating and environmental conditions.

Where is the Manifold absolute pressure sensor (MAP) Located on the Engine?

This image shows the location (arrowed) of the MAP sensor on a 2004 Honda CRV application. Note that while the actual locations of MAP sensors vary somewhat between applications, the appearance of MAP sensors will in all cases follow this general pattern, and be located directly on the intake manifold to bring it into direct contact with the volume of air inside the manifold.

This is an important difference between MAP and MAF (Mass Airflow) sensors that can sometimes resemble MAP sensors, although they have an entirely different function. Note, therefore, that MAF sensors can be located almost anywhere in the inlet tract, although MAF sensors are usually located either on, or just before the throttle body.

What Does the Manifold absolute pressure sensor (MAP) Look Like?

 

This image shows an example of a typical MAP sensor, such as might be found on many VW applications. Note though that while many MAP sensors might appear to be identical in all respects, MAP sensors have different calibrations to suit specific applications, and are therefore not interchangeable.

Moreover, while some MAP sensors have only three terminals in their connectors, MAP sensors that incorporate air temperature sensors have four terminals, meaning that the two types of MAP sensors are not interchangeable.

What are the Symptoms that the Manifold absolute pressure sensor (MAP) is Bad?

While the common symptoms of failed or failed MAP sensors are much the same across most applications, but note that the severity of one or more symptoms listed here could vary between vehicle makes and models, depending on the application and the nature of the problem. Nonetheless, some common symptoms could include one or more of the following-

  • Stored trouble code(s) and an illumined warning light
  • Poor acceleration, or a general loss of power that may or not vary based on engine speed and load
  • Excessive fuel consumption
  • The vehicle may surge, hesitate upon acceleration, or stall at low engine speed
  • In some cases, the engine may overheat as the result of an overly lean air/fuel mixture
  • A hard starting condition may be present
  • Depending on the application and the nature of the problem, some applications may exhibit severe misfires under some or all operating conditions
  • The vehicle may fail a mandatory emissions test

 

Note that failures and malfunctions of sensors, parts, and components other than the MAP sensor can also cause the above symptoms. Therefore, to avoid a misdiagnosis, pay careful attention to the OBD II fault codes that present themselves when these symptoms appear. Below is a list of the most common generic trouble codes that relate to MAP sensors-

  • P0068 – “MAP/MAF – Throttle Position Correlation”
  • P0069 – “Manifold Absolute Pressure – Barometric Pressure Correlation”
  • P0105 – “MAP Circuit Malfunction”
  • P0106 – “MAP/Barometric Pressure Circuit Range/Performance Problem”
  • P0107 – “Manifold Absolute Pressure/Barometric Pressure Circuit Low Input”
  • P0108 – “MAP Pressure Circuit High Input”
  • P0109 – “MAP / Baro Pressure Circuit Intermittent”
  • P1106 – “MAP/BARO Pressure Circuit Range/Performance Problem”
  • P1107 – “Barometric Pressure Sensor Circuit Low Voltage”

How do you test the Manifold absolute pressure sensor (MAP)?

Testing the operation of the MAP sensor is usually a simple, straightforward procedure that should be well within the capabilities of most non-professional mechanics. Simply follow the steps outlined below-

Step 1 – Locate the MAP sensor and verify that its electrical connector is properly secured and that all associated wiring is free of damage

Step 2 – If the connector and wiring appears to be undamaged, disconnect the connector

Step 3 – Switch on the ignition and use a digital multimeter to check the terminals on the harness side of the connector to see if one wire carries a 5-volt reference voltage. Note that you will require reliable service information for the affected application to determine the function and color-coding of the wires

Step 4 – If the correct voltage is present, reconnect the connector, and use proper back probing adapters to retest the signal wire, which is a different wire from the one that carries the reference voltage- refer to the service information to determine which wire is the signal wire

Step 5 – If no current is present on the signal wire, or the voltage is below one volt while the ignition is “ON” but the engine is NOT running, the MAP sensor is defective and it must be replaced with its exact equivalent to ensure proper operation of the engine management system.

Note though that while there are many aftermarket replacement sensors available, the wisest option, in this case, would be to use an OEM or at least an OEM-equivalent replacement sensor to ensure reliable and predictable operation of the replacement sensor.

How do you replace the Manifold absolute pressure sensor (MAP)?

Replacement of a MAP sensor is as simple as disconnecting the electrical connector, removing the retaining screws with suitable tools, and removing the faulty sensor from the manifold.

The steps to install the replacement sensor should happen in the reverse order of removal, but take extreme care when tightening the retaining screws that you do not over-tighten them, as doing this could damage the replacement sensor.

As the last step, double-check that the electrical connector is locked into position securely and that all wiring is secured to prevent wiring from chafing or rubbing against engine components.