What is a map sensor on a car?

Written by david mcguffin
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What is a map sensor on a car?
MAP sensors help to regulate the combustion in an engine. (Classic Car Engine Refurbished image by Janet Wall from Fotolia.com)

Car engines use a variety of sensors to help regulate the internal combustion process, including MAP (manifold absolute pressure) sensors, which partner with other sensors to help ensure the timing and efficiency of combustion. It is important to know the signs of MAP sensor failure as it pertains to your vehicle's performance as well as its ability to pass inspection in some states.

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Function

MAP sensors help measure and maintain the correct intake vacuum pressure in the air intake manifold. As the intake pressure changes while driving, the MAP sensor will change its voltage or frequency to adjust the rate of air intake. As a result, the proper mixture of air and gasoline are able to be mixed and exploded in the piston chamber to provide the energy for the internal combustion process. The MAP sensor is similar to older car components such as the vacuum advance diaphragm or the mechanical distributor.

Working With Other Components

Once the MAP sensor has obtained the information about the air pressure in the manifold, it sends that information to the car's computer to help regulate the amount of fuel that is pumped into the piston chambers. The MAP sensor also partners with the PCM (power-train control module), which helps regulate the air-fuel mixture ratio.

Appearance

The MAP sensor is near the air intake manifold and typically looks like a small, black, plastic box. The MAP sensor also has an electrical connection with wiring leading to the car's computer and uses vacuum lines that lead to the manifold. Some MAP sensors also have the appearance of having wings or are shaped like a fedora.

Troubleshooting

If you have noticed a loss of horsepower, torque and fuel efficiency, and your engine seems to be running badly, as indicated by occasional to frequent stall-outs, backfiring and slower acceleration from a stop, then your MAP sensor may have failed. A failing MAP sensor will also set off the check engine light on the dashboard, which will issue a code to an OBD II scanner requiring the MAP sensor to be replaced. However, it is also important to check vacuum lines as well as the electronic connections leading to the MAP sensor with a multimeter before replacing the MAP sensor.

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