Manifold Absolute Pressure (MAP) Sensor

by Abhishek Sohane, Clemson Automotive Engineering Graduate Student

Basic Description

Manifold Absolute Pressure (MAP) sensors provide information regarding the absolute pressure in the intake manifold to the engine control module. The engine control module needs to know the manifold pressure to control fuel delivery and engine timing. MAP sensors are generally located directly on the intake manifold or high in the engine compartment and connected to the intake manifold using vacuum hoses.

A typical MAP sensor consists of a ceramic or silicon diaphragm. This diaphragm is sealed on one side with a perfect vacuum or controlled pressure calibrated for the engine and on the other side it is exposed to the intake manifold. The silicon diaphragm is flexible. When the pressure in the intake manifold changes, the silicon diaphragm flexes, changing its resistance. The engine control module translates this resistance into a voltage. The voltage indicates the intake manifold pressure.

A MAP sensor is a 3-wire sensor. The three wires are the sensor ground, a 5-volt reference and a signal wire. At idle, the output of a MAP sensor is typically 0.85 volts to 1.3 volts.

Symptoms of a Faulty Map Sensor

1. Idling and Surging Problem

A faulty MAP sensor may affect the mixture of air and fuel to the extent that the engine will surge. The engine may also surge during idling. The engine will idle roughly i.e. the RPM will fluctuate when the car is on but not driving.

2. Spark Plug Fouling

The faulty MAP sensor may cause engine to produce a rich fuel mixture, causing spark plug to foul i.e. coat with a white powdery substance. Cleaning the spark plug will not be a solution until the MAP sensor is addressed.

3. Loss of Power

A MAP sensor may produce incorrect air-fuel mixture. If the engine has too much lean amount of fuel compared to the air in the cylinder, this will lead to improper combustion and in turn decrease engine power.

4. Increased Emissions

A faulty MAP sensor may cause to release excess of emissions.

MAP Sensor Checks

There are many methods to check a MAP sensor. One method is to use a scan tool to check for MAP sensor trouble codes. Second method is to observe the sensor’s output as a waveform on an oscilloscope and comparing it with the specifications in a manual.

Manufacturers

AC Delco, Airtex, Bosch, Continental, Delphi, Haltech, Napa Echlin, Wells

For More Information

[1] MAP Sensor, Wikipedia.

[2] Map Sensor Testing, YouTube, Mar 15, 2009.

[3] MAP or Manifold Air Pressure Sensor, YouTube, May 27, 2010.

[4] MAP Sensor & Wiring Diagram, YouTube, Jan 19, 2011.

[5] How to Troubleshoot a MAP Sensor, Dan Ferrell, eHow.com.