Many cars use a mass air flow (MAF) sensor to measure the amount of air entering the engine. When the device goes bad, it can lead to various symptoms, ranging from an illuminated check engine light to rough running and misfiring.
As you might guess, a bad MAF sensor can be a huge inconvenience. What’s more, the problem can damage other parts of your vehicle, such as the catalytic converter, if left unchecked.
So, if you think your MAF might be faulty, it’s a good idea to address the issue as soon as possible.
Because the MAF is a primary input to your car’s computer for fuel control (more on that later), the sensor can cause several noticeable symptoms when it fails. Some of the most common air flow sensor problems include:
Often, when there’s an issue with the MAF sensor, your car’s primary computer—often referred to as the powertrain control module (PCM)—will turn on the check engine light and store a diagnostic trouble code (DTC) in its memory.
Some of the most common MAF-related DTCs include P0100 through P0103. A faulty MAF sensor can also trigger other codes, such as those pertaining to an air/fuel ratio imbalance or an engine misfire.
Without an accurate signal from the MAF sensor, the PCM won’t know how much fuel to give the engine. That can either cause the engine to run rich (too much fuel) or lean (too little fuel). As a result, the combustion process—the ignition of the air/fuel mixture inside the engine—will be incomplete.
The outcome is an engine that runs rough and misfires.
A bad MAF sensor can trick the PCM into starving the engine for fuel. When that happens, the vehicle may exhibit a lack of acceleration. Similarly, a faulty MAF may cause your car to hesitate and stall.
A faulty MAF sensor can throw off your engine’s performance, leading to an increase in fuel consumption.
As was mentioned, the MAF sensor measures the amount of air entering the engine. The PCM uses the MAF sensor signal when calculating how much fuel to give the engine—more air equals more fuel.
There are several different types of MAF sensors found in different vehicles. The two most common designs are hot wire and hot film. Both types of sensors operate in a similar manner.
To measure airflow, the PCM continuously provides electrical current to heat the hot wire or hot film element. Airflow cools the element, reducing its electrical resistance, and creating an increase in current demand. The PCM uses the increase in current demand to determine the amount of air entering the engine.
It’s important to note that not all cars have a MAF sensor. Some models use what’s called a Speed Density System, instead. With this setup, the PCM uses input from the manifold absolute pressure (MAP) sensor and various other sensors when calculating fuel delivery.
A wide range of problems can mimic a bad MAF sensor, so it’s a good idea to test a suspect sensor before you rush out and buy a new one.
Before getting started, however, you’ll want to have the vehicle’s repair information handy. Manuals, such as those from Chilton, are good, but a subscription to a repair database (e.g, ALLDATA or Mitchel 1 DIY) is even better. You can find more information on accessing quality repair information in our article on repair manuals.
Note: The following are general guidelines for educational and entertainment purposes only. Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures.
If the check engine light is on, you’ll want to retrieve the corresponding diagnostic trouble codes using a scan tool or code reader. These days, you can even get an inexpensive code reader for your smartphone.
Is there a MAF-related DTC stored in the PCM’s memory? Then there may be a problem with the MAF sensor or its circuit. As was mentioned, air/fuel ratio and misfire codes may also point to a problem with the MAF sensor (though, there are many other possibilities, as well).
Keep in mind: Sometimes, a bad MAF sensor won’t set a code, especially on older vehicles with a type of self-diagnostics called OBD-1.
Next, you can move on to performing a visual inspection. You’ll want to look for issues, such as damaged wires and poor connections. Make sure that the MAF sensor’s electrical connector is clean and tight.
Repair any issues found during the visual inspection, clear the DTCs, and see whether the problem returns.
Testing a MAF sensor can be tricky. Hot wire sensors output an analog voltage signal, while hot film sensors create a square wave digital frequency pattern.
It’s important to know what type of sensor you have—and you should always consult the factory repair information before testing.
You can check the operation of both hot wire and hot film MAF sensors with a scan tool. A fancy scanner isn’t necessary for this step—you can use a basic tool, as long as it displays OBD live data.
The data parameter you want to view is usually labeled airflow rate and is measured in grams per second (g/s).
Here’s how it’s done:
Note: The idle airflow/engine displacement correlation is an imprecise, rule-of-thumb measurement that can vary by vehicle. Some automakers include the MAF sensor specifications in the factory repair information. It’s a good idea to consult a repair manual or repair database for this information.
Note: The transmission may need to be put into a lower gear to create a sufficient load on the engine.
Hot film MAF sensors output a digital waveform pattern that looks like little square humps. The frequency of the humps increases as air flow through the MAF increases.
To check the output of a hot film style MAF sensor, you’ll need either a digital multimeter with a frequency (Hz) setting, an OEM-level (i.e., expensive) scan tool, or an oscilloscope. The scope is the best choice since it allows you to see minor glitches in the MAF output signal.
Our sample vehicle for this test is a 1998 Chevy Astro with a 4.3L engine and a known good MAF sensor. Chevy’s specifications for the MAF sensor (with the van at operating temperature) are approximately 2285 Hz at 4.6 g/s. This value has some wiggle room and doesn’t need to be exact.
First, we can check the data on an OEM-level scan tool that offers manufacturer-specific live data. As we can see in the photo, our values (2512 Hz at 5.77 g/s) are close to the manufacturer’s specification (remember, there’s a little wiggle room).
You should also monitor the value while driving (with help from an assistant or recording function, of course). Typically, at WOT, the value should exceed 7 kHz.
Also, you can check the MAF’s frequency output using either a digital multimeter DMM with a frequency setting or an oscilloscope. A scope is the best option since it allows you to see the MAF signal directly.
To set up the scope, you’ll need a back probe test lead to connect to the MAF signal wire (see photo). You’ll want to attach the positive (red) lead to the MAF sensor’s signal wire, and the negative (black) lead to a good ground. Consult a repair manual or repair database to determine which wire is the MAF signal wire.
Next, turn on your scope and adjust the settings as needed. Then, start the engine and monitor the results at idle.
Judging from the waveform pattern in the image below, our Astro van’s MAF appears healthy. The sensor’s signal has humps that are nice and even. Plus, the frequency of those humps (2.42K Hz) is within specification.
Snap the throttle open by hand (or have an assistant operate the accelerator pedal). If the MAF sensor is working properly, the signal’s humps should still stay nice and even, but their frequency should increase.
Hot wire sensors produce an analog voltage signal that starts near zero volts. The sensor’s output voltage steadily climbs to around 5 volts as air flow through the MAF sensor increases.
To check a hot wire MAF sensor’s output, you’ll need either a regular DMM, an OEM-level scan tool, or an oscilloscope.
Our sample vehicle is a 2007 Honda Civic with a 1.8L engine and a known good MAF sensor. Because Honda does not list the MAF specifications for this car, we’ll have to use rule-of-thumb guidelines during testing.
The typical reading for an analog MAF sensor is around 1 volt at idle. As you can see in the image below, the sensor in our Honda is reading 1.31 volts at idle, which is just fine.
The MAF sensor signal voltage should steadily increase as the amount of air entering the engine increases. You can verify this by monitoring the value while driving (with help from an assistant or recording function, of course). Typically, at WOT, the value should be nearly 5 volts.
Good news: You can test a hot wire MAF using a traditional DMM. To set up the DMM, you’ll need a back probe test lead to connect to the MAF signal wire (see photo). You’ll want to attach the positive (red) lead to the MAF sensor’s signal wire, and the negative (black) lead to a good ground.
Consult a repair manual or repair database to determine which wire is the MAF signal wire.
Next, start the engine and monitor the results at idle. Judging from the readings in the image below, the Civic’s MAF output at idle appears fine. The reading is close to 1 volt at idle.
Open the throttle by hand (or have an assistant operate the accelerator pedal). The voltage should steadily increase as airflow increases.
In some instances, what seems like a bad MAF is actually a problem somewhere in the sensor’s circuit. So, if your test results point to a bad MAF, but replacing the sensor doesn’t cure the problem, you’ll need to dig a little deeper.
Consult a repair manual or a repair database for the factory wiring diagram. Then use a DMM to ensure the supply voltage and ground portions of the MAF circuit are intact. You may also need to check for continuity between the MAF sensor and the PCM.
Although somewhat rare, it’s also possible for the PCM to misinterpret the MAF signal. The dealer may have a technical service bulletin (TSB) suggesting a software update to fix the problem.
In some cases, you can clean the MAF sensor to restore normal performance. You can clean the device using a dedicated cleaner that comes in an aerosol can.
What You Need to Clean a Mass Air Flow Sensor:
The tools and supplies needed to clean a MAF sensor vary, depending on what type of car you have. But, in general, you’ll need:
When cleaning the MAF sensor, you should always follow the instructions listed on the product you purchased. In general, however, the process involves the following:
Warning: Do not use MAF cleaner on Karman-Vortex style MAF sensors. This type of sensor uses either an ultrasonic receiver or a pressure sensor to detect vortexes in the airflow through the sensor.
1. Put on your safety glasses.
2. Locate the MAF sensor (positioned between the air filter assembly and throttle body).
3. Disconnect the MAF sensor electrical connector.
4. Use a screwdriver to loosen the clamps on the air intake duct.
5. Remove the MAF sensor by pulling it out of the air intake duct.
6. Place a clean towel under the MAF sensor.
7. Attach the straw to the aerosol can. Then spray the recommended amount of cleaner (as listed on the product instructions) onto the sensing element inside of the MAF housing.
Note: Do not allow the straw to contact the MAF sensing element.
8. Allow the MAF sensor to dry thoroughly.
9. Reinstall the MAF sensor into the air intake duct.
10. Use a screwdriver to tighten down the clamps on the air intake duct.
11. Reconnect the MAF electrical connector.
Sometimes, cleaning the MAF doesn’t work and you have to replace the sensor. The steps for replacement are the same as those involved in removing and reinstalling the sensor for cleaning.
The process for your actual vehicle may vary. But replacing the MAF typically involves the following steps.
Although in some cases, you may technically be able to continue driving with a bad MAF sensor, you should address the issue as soon as possible. A faulty MAF can damage other parts of your vehicle, such as the catalytic converter.
What’s more, some cars won’t even run when the MAF fails. In other instances, the engine will run but run poorly, making the vehicle difficult to drive.
Driving with a malfunctioning mass airflow sensor may damage your catalytic converter, increase harmful vehicle emissions, and making your engine run poorly. Thankfully, getting a replacement is easy with CarParts.com.
The best part? You don’t even have to leave your home to get your hands on a new sensor. Shopping is quick and hassle-free when you order the parts you need online. Choose from our selection of top aftermarket brands, and enjoy competitive pricing for high-quality parts.
Shop now, and get your new mass airflow sensor delivered straight to your doorstep in as fast as two business days.
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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I have a suziku areio 2.0L and ill start the car and idles poor and whenever i try to give it a gas it bogges out and dies can someone plz help i put ne fuel pump i have been told that my MAF sensor is bad thank you
what type of MAF sensor can i use in my 2010 Mazda Premacy?
Hello,
The Mazda Premacy is called the Mazda 5 here in the United States. Does your car have a 2.3L engine? If so, take a look at your MAF and see if looks like any of these sensors for a 2010 Mazda 5: https://bit.ly/2Eppp4x