What Is a Manifold Absolute Pressure (MAP) Sensor?

A manifold absolute pressure (MAP) sensor is an important component of nearly all fuel-injected vehicles. Whether you drive a car, truck or SUV, it will likely feature a MAP sensor -- assuming it has a fuel-injection system. MAP sensors, however, can fail. To better understand the purpose of this component, as well as signs of failure, keep reading.

An Introduction to MAP Sensors

MAP sensors are electrical components that are designed to regulate the delivery of fuel into the engine's combustion chamber. Fuel-injected vehicles, of course, have nozzles that spray fuel into the engine's combustion chamber. Known as fuel injectors, they work in conjunction with a MAP sensor. The MAP sensor will collect information while calculating how much fuel the injectors need to spray into the engine's combustion chamber.

How MAP Sensors Work

How do MAP sensors work exactly? They consist of small electrical components that are connected to the vehicle's engine control module (ECM). Upon cranking up your vehicle, the MAP sensor will begin to measure the intake manifold pressure. It will then convert these readings into electrical signals, which the MAP sensor will send to your vehicle's ECM.

When your vehicle is idling, the intake manifold will have minimal pressure. When you press on the gas pedal, the intake manifold's pressure will increase. The MAP sensor's job is to detect these pressure changes and convert them into electrical signals. An increase in pressure means that the injectors should spray more fuel into the engine's combustion chamber. The MAP sensor will detect pressure changes in the intake manifold so that the injectors deliver an appropriate amount of fuel.

Signs of MAP Sensor Failure

MAP sensor failure can manifest in a several ways. Rough idling, for instance, is a common sign of MAP sensor failure. The MAP sensor may detect an incorrect amount of pressure in the intake manifold, resulting in rough idling.

You may experience poor gas mileage if your vehicle's MAP sensor has failed or is beginning to fail. MAP sensors can fail in different ways. If your vehicle's MAP sensor believes the pressure is lower in the intake manifold than what it really is, it may cause the engine to run rich. Rich-running engines, of course, consume an excessive amount of fuel. The end result is poor gas mileage.

In addition to running rich, MAP sensor failure can cause your vehicle's engine to run lean. Lean-running engines are those that consume an insufficient amount of fuel. They have an abnormally high air-to-fuel ratio.