Manifold Absolute Pressure (MAP) Sensor

by Nitin Budhiraja, Clemson Automotive Engineering Graduate Student

Basic Description

The Manifold Absolute Pressure (MAP) sensor is a part of the Engine control module. It provides information about manifold pressure to the engine control unit.

The MAP sensor continuously compares atmospheric pressure to the intake manifold vacuum and generates a corresponding voltage signal for the difference and sends it to the Engine Control Unit. It works with a 5 volt input signal and there is a silicon chip which changes its resistance based on the pressure which in turn varies the voltage between 1 to 4.5 V and then sends the voltage signal to ECU.

The ECU takes this voltage and then determines if it needs to increase or decrease the supply of fuel for optimum combustion. In case of low engine load condition, the ECU cuts down the fuel supply and increase the timing between two sparks from the spark plug whereas in case of high engine load or when the car is on slope; it increases the supply of the fuel and reduces the time between two consecutive sparks from the spark plug.

Symptoms of a bad MAP sensor

1. Poor Engine Performance

If the MAP is sending faulty signals to the ECU, then the imbalance in the actual and sensed air pressure difference will lead to rough engine performance. It would be mostly visible on accelerating and braking when the difference in the two air pressures is maximum. Rough idling of the engine is usually observed when the MAP is faulty.

2. Excessive emissions

Another symptom of a faulty MAP sensor is a lower fuel economy and more emissions. This is because the fuel supply is not cut off when required.

3. Engine Surging

A faulty MAP sensor can lead to poor synchronization between air intake and release of fuel. This would result in delayed acceleration followed by a sudden surge.

4. Fouled spark plug

The engine would either run rich or lean depending upon the faulty signals from the MAP sensor. If it is running rich, then the spark plugs could become fouled (coated with residue) due to the improper combustion.

Manufacturers

Bosch, Adelco, Delphi, Napa, Haltech

For More Information

[1] Map Sensor, Wikipedia.

[2] What Are the Symptoms of a Bad Map Sensor?, Tom Pace, EHow.com, Dec 06, 2010.

[3] MAP Sensor, YouTube, Feb. 21, 2011.

[4] MAP Sensor Testing, YouTube, Mar. 15, 2009.

[5] MAP Scanner, Wiring & Electric Tests,YouTube, Jan. 16, 2011.

[6] MAP Sensor,OBD codes website.

[7] How to Troubleshoot a MAP Sensor, Dan Ferell, EHow.com, Feb. 9, 2011.