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Summary
  • The manifold absolute pressure (MAP) sensor is a small transducer that provides the ECM/PCM with input on the prevailing pressure in the intake manifold. Older MAP sensors were remotely mounted and read manifold pressure/vacuum through a hose connected to the intake somewhere behind the throttle plate. More recently, the MAP sensor is mounted to an intake port with an o-ring, eliminating the need for a connecting hose.
  • The MAP sensor may malfunction if the electronics are fried due to intense heat (which would indicate much deeper problems than just a bad sensor), if it suffers physical damage, if there’s excessive vibration in the engine bay, and if the hose that it’s connected to is loose, cracked, or swollen.
  • Some symptoms to keep an eye out for include poor fuel economy, power deficiency, and rough idling.

What’s a MAP Sensor?

The MAP sensor reads barometric pressure when the key is first switched on (because this is what’s in the manifold when the engine isn’t running), then switches to measuring manifold absolute pressure after the engine starts. Color that “manifold vacuum,” which is a solid indicator of engine load and needed fuel.

map sensors either mounted in the manifold or connected to it with a hose
MAP sensors take many different forms (here are just a few), and are either mounted in the manifold or connected to it with a hose. | Image Source: Richard McCuistian

The engine controller uses the initial barometric pressure reading in its algorithms as a baseline and the dynamics of manifold vacuum for engine load and EGR flow. Where there is a mass airflow sensor (MAF) and a MAP sensor, the MAP sensor provides secondary input (like for EGR flow detection) and provides a backup input in case the MAF sensor goes offline.

, How to Check if Your MAP Sensor is Bad

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: You can access the MAP sensor input using a scan tool and if you suspect a bad sensor, an A-B-A swap while watching the datastream on the tool is a good method. Make sure you clear the adaptive tables in the ECM/PCM by removing the negative battery cable for about 5 minutes while installing the test MAP sensor.

A MAP sensor fails when:

  • It is contaminated, clogged, or damaged
  • Its electronics are fried due to intense heat in the engine compartment
  • There is too much vibration in the engine compartment
  • The sensor is physically damaged
  • The hose it connects to is cracked or swollen
  • Its connection with the hose is loose
, How to Check if Your MAP Sensor is Bad

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Older Ford MAP sensors read hertz rather than voltage; about 159 hz at sea level without the engine running and about 110 hz with the engine idling in park.

Signs of a Bad MAP Sensor

So what happens when your MAP sensor has gone kaput? Here are the most common consequences:

Decline in fuel economy

If your car’s computer inaccurately reads the pressure in the intake manifold as high, the engine will inject more fuel to meet the heightened engine load. This can reduce fuel economy and possibly lead to detonation.

Power deficiency

On the flip side, if your car’s computer presumes pressure in the intake manifold is low, it will do the reverse and cut down fuel consumption, therefore leaving the engine with less power for acceleration.

Rough idling

When fuel injection is inadequate, the engine tends to idle rough. There’s also a chance for cylinder misfire to occur.

“Check Engine” light comes on

When the “check engine” light illuminates, it’s possible there’s something wrong with your MAP sensor. This is also the perfect time to check if there’s any problem with the other sensors in your car.

Failed emission tests

If your MAP sensor is unreliable, chances are, the emissions discharged from your tailpipe will be filled with hydrocarbons, nitrogen oxides, and carbon monoxide. This automatically causes you to fail your emissions test.

It helps to be aware of the signs of a bad MAP sensor so you can act fast to remedy the problem. Or, better be proactive by inspecting your MAP sensor during routine maintenance checkups. You can use a scan tool for this (your MAP sensor reading at idle should have a reference voltage close to five volts) and administer a bench test using a hand vacuum pump and a voltmeter.

Make it a habit to check your MAP sensor from time to time to maintain a sense of balance in your engine’s operation and ensure optimum performance for your car.

Where to Get a New MAP Sensor for Your Vehicle

If you’ve confirmed that you have a bad MAP sensor, don’t put off shopping for a replacement. The issues it can cause for your ride are no joke, as they can make driving difficult and dangerous. For a high-quality MAP sensor that won’t break the bank, we have you covered here at CarParts.com.

All our products come with a low-price guarantee, so even if you’re shopping on a budget, you’re sure to get the best value for your money. Rest assured that you’ll get a MAP sensor replacement that’s built tough. After all, all our parts passed the highest quality control standards from industry professionals.

If you want to repair your ride as soon as possible, you can count on our fast and reliable shipping. Get your new sensor in as fast as two business days, thanks to our strategically located warehouses across the country.

Check out our catalog today!

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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