How to Check if Your MAP Sensor is Bad

If you suspect your vehicle’s manifold absolute pressure (MAP) sensor is faulty, you can inspect it for issues. It’s typically plugged into the intake manifold, which refer to the hoses or plastic assembly that leads air into the engine. Sometimes, the MAP sensor can also be on the throttle body.

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

Not all issues can be seen at a glance. There’s a chance you won’t spot anything physically wrong with your MAP sensor when you inspect it. A great way to check your MAP sensor is to test it with a multimeter.

How to Test the MAP Sensor With a Multimeter

A MAP sensor typically has three prongs where wires connect.

The first prong receives a 5-bolt reference voltage from the electronic control unit (ECU), while the second prong is a ground wire that leads to a ground source. The third prong is a signal wire that leads to the ECU. You must splice into the wires that connect to these prongs to test them with the multimeter.

Set the ignition switch to the “ON” position, then find the voltage and signal wires. With the multimeter set to its 20-volt direct current (DC) setting, connect the red or negative probe to the wires connected to the MAP sensor. The multimeter’s black or positive probe must be connected to a nearby ground source like the engine.

Using the red probe, find the reference power wire and signal wire. The power wire must always read 5V. Meanwhile, the signal wire voltage varies depending on the sensor’s readings.

Turn on the engine, then check whether the voltage fluctuates when you rev the engine. The voltage should vary between 1 and 2 volts, and the voltage must drop whenever you apply the throttle.

If the voltage doesn’t fluctuate or if the signal wire doesn’t have voltage, then the MAP sensor has an issue.

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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.

What’s a MAP Sensor?

What does a MAP sensor do in a car? 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.

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.

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.

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.

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