How does an auto exhaust map sensor work?

Written by jay motes
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How does an auto exhaust map sensor work?
The MAP sensor measures air intake pressure in a car's engine. (engine image by goce risteski from

The manifold absolute pressure, or MAP, sensor plays a vital role in keeping an engine operating at peak efficiency. Without a properly functioning MAP sensor, an automobile engine will run poorly or may fail to run at all.


The MAP sensor measures air pressure inside an automobile's intake manifold. The level of air pressure depends on how hard the engine is working. Under heavier loads, the engine uses more air, which reduces the pressure in the manifold. The engine's computer uses the amount of pressure measured by the sensor to adjust the fuel injection and ignition timing.

Signs of Problems

A defective MAP sensor results in poor engine performance. Typical symptoms of MAP sensor failure include rough idle, stalling, spark plug "knocking" and an increase in fuel consumption. Auto-parts stores sell diagnostic scan tools, which determine if a MAP sensor's working properly.


A defective MAP sensor requires replacement. Manufacturers calibrate MAP sensors for specific models and engines, so car owners should note the type needed before purchase. When replacing the MAP sensor, drivers should also inspect the vacuum hose attached to it, and replace a hose showing cracks or other damage.

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