What is a manifold absolute pressure sensor and where is it located?

A manifold absolute pressure sensor, commonly abbreviated to MAP sensor, is used in some fuel injection engines to determine the pressure in the intake manifold, and then provides a signal on engine load to the vehicle’s engine control unit (ECU). The ECM uses this data to calculate air density and determine the engine's air mass flow rate. This information, along with information from an engine speed sensor and an air temperature sensor, is then used by the ECU to adjust fuel flow and ignition timing in order to keep the engine running smoothly. Fuel injection engines usually have either a MAP sensor or a mass air flow (MAF) sensor, but rarely will have both. In vehicles that are turbocharged or supercharged, the MAP sensor also reads the amount of boost pressure.

The MAP sensor has a vacuum tube attached to the intake manifold and a vacuum or calibrated pressure area. Between them is a silicon chip that flexes due to the pressure difference between the two areas. This changes the flow of voltage through the chip, which is received as a signal by the ECU. The sensor is usually found on the intake manifold itself, or somewhere close to it. 

How do I know if my MAP sensor needs to be replaced?

Like anyone else who works under a lot of pressure, the MAP sensor can eventually wear out. The ECU can detect voltage outside the usual range coming from the MAP sensor and will activate the check engine light in response. You may see the check engine light come on intermittently, during acceleration or starting, since those are the times when it is most necessary to maintain proper fuel flow and timing. 

A malfunctioning MAP sensor can cause problems with fuel flow and timing that may cause the engine to run rough. You may experience engine surging or hesitation. You may also experience incomplete combustion which can affect fuel mileage and emissions. You may see a drop in gas mileage, fail an emissions inspection, or see thick black smoke coming out of your car or truck’s tail pipe. The uncombusted fuel can also foul your spark plugs. 

These problems may also be caused by vacuum leaks in any of the hoses attached to the intake manifold. It’s best to check that the MAP sensor is the cause of your problem before replacing it. The wiring and electronic components of the MAP sensor can be tested with a multimeter. It’s also possible to check that the MAP sensor is functioning with a vacuum tester. If your check engine light has come on, a mechanic with a diagnostic scan tool can see what problem code the ECU is reporting. Codes P00068 and P00069, as well as codes P0105 through P0109, can indicate a faulty MAP sensor, as shown below.

OBDII Check Engine Codes related to MAP Sensors

P0068 MAP/MAF - Throttle Position Correlation
P0069 Manifold Absolute Pressure - Barometric Pressure Correlation
P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem
P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input
P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

Can I replace a MAP sensor myself?

Once you’ve determined that the MAP sensor is the source of your problem, replacing it will be quite easy. The MAP sensor should be easily accessible on your intake manifold. You’ll just need to disconnect its wiring harness, unbolt it, remove it, and install the new one by reversing the removal procedure.