How to Troubleshoot a Mass Airflow Sensor

Updated on September 23, 2016

I. MAF Sensor Operation

Basically, the MAF sensor—also known as airflow meter—measures the amount of air flowing into the engine through the air cleaner assembly, which contains the air filter and connects to the throttle body.

Depending on the make and model, your car uses either a hot-wire (the most common) or a hot-film type airflow meter. Different design, same function: Tell the computer how much air is flowing into the engine. The computer uses this information, along with input from other sensors, to provide the correct amount of fuel to the engine at any given time.

The hot-wire type sensor maintains a wire (located in the middle of the airstream) at a higher temperature than the air flowing in. To maintain this predetermined temperature, electric current to the wire increases as airflow increases.

In general, the hot-film type sensor works the same way except it uses a film instead of a wire to send the signal to the computer.

It is this extra amount of current the sensor is using that tells the computer how much air is flowing in. In other words, the faster you drive, the higher the cooling effect on the hot wire or film, the more current flowing to the sensing element.

So you can use the sensor operating logic to conduct your tests.

Here, we'll go over the steps you need to troubleshoot a hot-wire type MAF sensor using a digital multimeter (DMM) to read the voltage signals. Testing a film-type sensor is no different, except that you check for frequency signals instead of voltage. For this, you'll need a digital multimeter (DMM) or an oscilloscope that can read frequencies. Other than that, the next steps apply.

Typical mass airflow (MAF) sensor.
Typical mass airflow (MAF) sensor. | Source
I. MAF Operation
Bad MAF Sensor Symptoms
II. Troubleshooting a Mass Air Flow Sensor
CAUTION - Can You Cause Electrical Damage With Your DMM?
A) How to Test the MAF Circuit for Power and Ground Signals
B) How to Test the MAF Sensing Element for Continuity
C) How to Test the MAF Sensor Voltage Signals
How to Save Time in MAF Sensor Diagnostics
III. MAF Sensor Tests Results
How to Install a New MAF Sensor

Installing a new mas airflow (MAF) sensor to see if it'll fix your engine driveability problems is not a good diagnostic approach. You can spend around $100 or more on a quality airflow sensor and yet solve nothing. But you can learn how to troubleshoot one in a few steps following this simple guide.

Here, you'll see what is the most common problem affecting MAF sensors (and what to do about it), what you need to pay attention to during your troubleshooting procedure, and, finally, find out whether you are dealing with a bad sensor.

Before we jump into the diagnostic, though, let's take a look at how the MAF sensor works so the procedure makes sense to you.

Bad MAF Sensor Symptoms

You may have a bad MAF sensor if you notice one or more of the following symptoms:

  • Decrease in engine power
  • Engine vibrates (poor idling)
  • Engine hesitates or stalls at acceleration
  • More frequent stops at the gas station
  • Engine surges at idling
  • Diagnostic trouble codes pointing to the MAF sensor
  • Other driveability problems

On some vehicle models, the MAF sensor also informs the computer on air intake temperature and engine load (to control some automatic transmission functions) so the number of symptoms increases.

However, you can hardly diagnose a MAF sensor on symptoms alone. Other faulty components can also produce these same symptoms, like the fuel pump, fuel pressure regulator and vacuum system. Thus, the need to troubleshoot the MAF sensor (and related circuits as needed) before replacing components.

Use a DMM with at least 10 Megaohm of impedance.
Use a DMM with at least 10 Megaohm of impedance. | Source

II. Troubleshooting a Mass Air Flow Sensor

So now that you have a broad knowledge of how an airflow meter works, you are ready to test the MAF sensor. So let's get ready.

1. First, open the hood of your vehicle and locate the MAF sensor on the air cleaner assembly. Usually, you'll find it between the air filter housing and throttle body. This could be a small block or a cylindrical section mounted as part of the air duct. On some models, you'll find it inside the filter housing.

2. Look for an electrical connector on the air duct right after the air filter housing. If you have difficulty locating the sensor, look it up in the vehicle repair manual for your particular vehicle make and model.

3. To test the MAF sensor, you'll need to have the electrical connector plugged in to the sensor. So check if you can backprobe the wires. If not, you'll need to pierce the wires using a pin when conducting your tests. If you use the later method, wrap the pierced wires with electrical tape when you're done with the tests to prevent rust from creeping into the wires.

4. Identify the power, ground(s), and signal wires on the electrical connector. Check your repair manual, ask at your local auto parts store, or search online for this information. Sometimes, you can identify these wires by testing them as described later. So even if you don't have this information at hand, go ahead with the tests anyway.

Now, we'll look at the steps to test a hot-wire type MAF sensor using a digital multimeter by reading its voltage signals. Remember that testing a hot-film type sensor is basically the same except you are reading frequency (Hz) signals. If you don't know what type of sensor you have on your vehicle, consult your vehicle repair manual, ask at your local auto parts store, or search online for the MAF sensor for your particular vehicle make and model and read through the description.

CAUTION - Can You Cause Electrical Damage With Your DMM?

Yes. When troubleshooting electronic car components with a digital multimeter, always use one with at least 10 Megaohm impedance protection. This prevents the meter from drawing too much current and destroying sensitive electronic devices.

A) How to Test the MAF Circuit for Power and Ground Signals

Here, you check that your car computer is actually sending power to the airflow meter and grounding the circuit.

1. Unplug the MAF electrical connector. Visually inspect the electrical connector and terminal for dirt or damaged. Gently pull at the wires to check for tightness. A dirty, burnt, contaminated or loose wire will interfere with the sensor signals.

2. Set your digital meter to 20 Volts DC (direct current) or close to it.

3. Connect your meter red probe to the connector power terminal (on the side going to the computer) and the meter black probe to ground (this could be on the engine block, an unpainted bracket or the negative (black) terminal on your car battery).

4. Turn the ignition key to the ON position, but don't start the engine.

5. Your meter should read between 10 and 13 volts, close to battery voltage. If not, you may have a fault in that part of the circuit between the electrical connector and the car computer.

6. Now, connect your meter black probe to the ground on the connector terminal (on the side going to the computer) and the meter red probe to battery positive (+) terminal.

7. Your meter should read between 10 and 13 volts, close to battery voltage. If not, you may have a fault in that part of the circuit between the electrical connector and the car computer.

8. Turn off the ignition key.

MAF sensor cleaning.
MAF sensor cleaning. | Source

B) How to Test the MAF Sensing Element for Continuity

1. Now, identify the terminals on the MAF sensor itself that correspond to the signal wire and ground.

2. Set your meter to continuity or the lowest setting on the Ohms scale.

3. Connect one meter probe to signal and the other probe to ground on the MAF electrical connector, polarity doesn't matter here.

4. You should read 0 (or close to 0) ohms of resistance. If your meter reads infinite resistance, probably the MAF sensing element burned or broke. Visually inspect the sensor.

C) How to Test the MAF Sensor Voltage Signals

1. Plug back in the MAF electrical connector.

2. Set your meter to 10 DC V (or close to it).

3. Start and let the engine idle.

4. Backprobe the signal and ground wires (red probe to signal and black probe to ground).

5. Depending on your MAF sensor, your voltage reading should be between 0.60 to 0.80 volts at idle (if your reading indicates 12 volts or pretty close to it, you are probing the power wire, not the signal wire).

6. Increase engine speed between 2,500 and 3,500 RPMs by manually opening the throttle plate, or ask an assistant to depress the accelerator pedal. Your voltage should increase to about 1.5 to 3.0 volts. Remember that Increasing engine speed increases airflow.

7. On a piece of paper jot down your voltage readings. Also, note whether the signal jumped, skipped, responded slowly, or travel smoothly and fast upon increasing engine speed. Head over to the Results sections below.

How to Save Time in MAF Sensor Diagnostics

On some newer vehicle models, the car computer can produce precise diagnostic trouble codes (DTCs) that can help you pinpoint the cause of the problem more accurately and faster. So make sure to scan the computer for potential DTCs.

A bad MAF sensor may cause the engine to stall.
A bad MAF sensor may cause the engine to stall. | Source

III. MAF Sensor Tests Results

Now, compare the results of your voltage (or frequency) readings to the specifications in your vehicle repair manual.

Usually, a slow response or no response from the MAF sensor means one of three things:

  • The MAF sensor has failed.
  • The hot wire or film element is dirty or damaged, unable to 'feel' airflow.
  • The sensor self-cleaning electrical circuit (on hot wire types) has failed.

By far, the most common cause of MAF sensor failure is a dirty sensing element. Depending on your specific results, you may want to check the sensor itself:

  1. Disconnect the MAF sensor from the air cleaner assembly and visually inspect the sensing element.
  2. If the sensing element is dirty, the sensor might actually be working but contamination is preventing it from doing its job.

Hot-wire type sensors have a self-cleaning electrical circuit that heats the sensing element up to 1000 C degrees (1832 F) when you shut off the engine. If that part of the circuit fails (not uncommon), the sensor will end up covered in dirt and eventually fail to read incoming air. A couple of quick checks is to take a look at the circuit fuse and test the relay that controls the self-cleaning circuit. Use this guide How to Test a Fuel Pump Relay and Other Automotive Relays to check the relay in the circuit. If necessary, consult your vehicle repair manual to locate the relay.

Also, you may want to try cleaning the sensing element with MAF sensor cleaning spray. Avoid touching the sensing element, and never clean a sensing element with a rag or cleaners not intended for a MAF sensor or electrical contacts. Follow the product manufacturer instructions, and retest the MAF sensor following the previous steps.

If cleaning the MAF sensor with the cleaning solution solves the problem, then:

  • You may have a problem with the self-cleaning circuit
  • An air leak around the cleaning assembly is bypassing the air filter.
  • A low quality filter is shedding material and sticking to the sensing element.
  • An air leak around the air filter housing (a crack on the filter housing or improperly installed filter cover or loose clamps) is introducing unfiltered air and contaminating the sensing element.

What if your tests indicate a good MAF sensor?

  • If your tests didn't reveal something wrong with the sensor or the circuit but your computer says there's something wrong with it, check the part of the air cleaner assembly between the sensor and the throttle body. Air leaks will trick the computer into thinking the sensor has failed.

But my results seem inconclusive, what do I do?

  • Check with your dealer or online car forums dedicated to your vehicle make and model for a possible technical service bulletin (TSB) related to your problem. Technical problems with the design or materials used in the MAF sensor or circuit can show up after miles of driving.

How to Install a New MAF Sensor

If your tests indicate a bad MAF sensor, you can replace it yourself in a few minutes. In most vehicle models, all you have to do is:

  • disconnect the part of the air intake duct that connects to the MAF sensor;
  • carefully unplug the sensor electrical connector;
  • unscrew two or more sensor mounting bolts;
  • remove the old sensor; and
  • install the new one.

Further Investigation

Most of the time, your tests results will lead you to the nature (or cause) of the problem in a few minutes. For example, if a sensor fails to respond to an incoming signal, you know that the problem lies with the sensor itself.

Other times, the results may not take you too far, especially if you don't have much experience in car repair. When this happens, you can visit one or more forums dedicated to your specific vehicle make where you can communicate with other drivers that might've faced this same type of problem.

However, if your tests proved your MAF sensor works as expected, perhaps you're dealing with a fuel, ignition, or vacuum related problem.

Most of the time, though, you'll be able to find the cause of the problem, make the repair, and get your car back on the road sooner than you thought possible.


    0 of 8192 characters used
    Post Comment

    • Dan Ferrell profile image

      Dan Ferrell 2 months ago

      Provided the installation was done correctly, there's no air-flow leaks (you connected the air cleaner ducts tight) and you have a clean MAF connector, there could be several reasons for this code reappearing:

      * Make sure to clear the computer codes

      * Sometimes, using non-OEM parts can cause the CEL to come on.

      * On some models, it takes weeks or months for the computer to relearn the best engine driveability-performance. So you need to be patient.

      Good luck

    • profile image

      Dan 2 months ago

      2 months ago engine diagnosis showed the MAS was bad and it was replaced with a new quality unit. Now the check engine lite came back on indicating the MAS. Any sugestions?

    • Dan Ferrell profile image

      Dan Ferrell 2 months ago

      Hi King,

      have you scan the computer for DTCs (trouble codes). Usually a problem with this sesnor will be caught by the computer. The codes should give a directon where to go looking.

      Good luck

    • profile image

      Kingwiredu 2 months ago

      My car normally intermittently start. At a point when is not stating and upon removing crankshaft speed sensor, car then starts. Crankshaft sensor has been changed but still problem keep coming intermittently.

      Can some one assist me?

    • Dan Ferrell profile image

      Dan Ferrell 6 months ago

      Hi HM,

      Check the MAF sensor for dirt or contamination,

      Another sensor that may cause this symptom is the Idle Air sensor on the throttle body. Try unplugging this sensor as well ans see what it does.

      Good luck

    • profile image

      Haziq M 6 months ago

      Hi.. merc e230 w210. The car hesitate and idle surge between 1000 to nearly 0 when accelerator pedal off. When I open up hood, and pull off the MAF sensor. The engine still runs. Is it bad MAF sensor? Thanks.

    • profile image

      msw 14 months ago

      I read somewhere that at idle that the number of grams/sec shown on the OBD tool is equivalent to the size liter engine. Thus, a 3.6L engine would show about 3.6 grams/sec of air flow by the MAF sensor. Hence knowing your engine size one would know if the MAF is measuring intake airflow correctly or not. If less then a cleaning should improve fuel efficiency.

    • Dan Ferrell profile image

      Dan Ferrell 14 months ago


      Glad it helped

    • profile image

      Dan 14 months ago


      Glad it helped

    Show All Categories