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How to Troubleshoot a Mass Airflow Sensor

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A bad MAF sensor may cause the engine to stall.

A bad MAF sensor may cause the engine to stall.

You might be thinking of installing a new mass airflow (MAF) sensor to see if it'll fix your engine driveability problems. But it's not a good diagnostic approach to just replace the sensor without investigating. You can spend $100 or more on a quality airflow sensor and yet solve nothing. But you can learn how to troubleshoot a MAF sensor in a few steps by following this simple guide.

Here, you'll see:

  • the most common problem affecting MAF sensors (and what to do about it),
  • how to find out whether you are dealing with a bad sensor,
  • and what you need to pay attention to during your troubleshooting procedure.
Typical mass airflow (MAF) sensor.

Typical mass airflow (MAF) sensor.

Topics in This Article

1. Symptoms of a Bad MAF Sensor

2. How the MAF Operates

3. Troubleshooting a Mass Airflow Sensor

  • 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 MAF Sensor Voltage Signals

4. MAF Sensor Test Results

5. How to Install a New MAF Sensor

1. Symptoms of a Bad MAF Sensor

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

  • A decrease in engine power
  • The engine vibrates (poor idling)
  • The engine hesitates or stalls at acceleration
  • More frequent stops at the gas station
  • The engine surges at idling
  • Other driveability problems
  • You get diagnostic trouble codes pointing to the MAF sensor

On some vehicle models, the MAF sensor also informs the computer about air intake temperature and engine load (to control some automatic transmission functions). So a bad MAF sensor on these cars can cause an even wider range of symptoms.

You can hardly diagnose a MAF sensor on symptoms alone. Other faulty components, like the fuel pump, fuel pressure regulator, and vacuum system, can create similar symptoms. That's why you need to troubleshoot the MAF sensor (and related circuits as needed) before replacing components.

2. How the MAF Works

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

Basically, the MAF sensor 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 airflow meter (the most common) or a hot-film type. Different design, same function: it tells 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, and so 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.

Use a DMM with at least 10 Megaohm of impedance.

Use a DMM with at least 10 Megaohm of impedance.

3. Troubleshooting a Mass Airflow Sensor

Now that you have a broad knowledge of how an airflow meter works, you are ready to test the MAF sensor. 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 into 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 latter 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 rather than voltage. 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, you can. 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 damage. Gently pull on the wires to check for tightness. A dirty, burnt, contaminated, or loose wire will interfere with the sensor signals.
  2. Set your digital meter at or close to 20 Volts DC (direct current).
  3. Connect your meter's red probe to the connector power terminal (on the side going to the computer) and the meter's 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's black probe to the ground on the connector terminal (on the side going to the computer) and the meter's red probe to the battery's 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.

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 is burnt or broken. Visually inspect the sensor.

C) How to Test the MAF Sensor Voltage Signals

  1. Plug the MAF electrical connector back in.
  2. Set your meter at or close to 10 V DC.
  3. Start the engine and let it 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 the engine speed increases airflow.
  7. On a piece of paper, jot down your voltage readings. Also, note whether the signal jumped, skipped, responded slowly to increased engine speed, or responded quickly and smoothly. Head over to the Results sections below.

4. Interpreting the Results of Your MAF Sensor Test

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

If the MAF Sensor Responds Slowly or Not at All

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 so that it is unable to 'feel' air flow.
  • The sensor self-cleaning electrical circuit (on hot-wire types) has failed.

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 quick check is to take a look at the circuit fuse and then 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's instructions, and retest the MAF sensor following the previous steps.

If Cleaning the MAF Sensor Solves the Problem

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.

If Your Tests Don't Find Anything Wrong With the 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.

If Your Results Seem Inconclusive

If you don't know how to interpret your results, check with your dealer, or on 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.

5. 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.
  • Install the new one.

Further Investigation

Most of the time, your test results will lead you to the 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.

If your tests prove that 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.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: It is true that if you unplug the MAF sensor and the engine is still running then the sensor is bad?

Answer: Removing the sensor helps to diagnose a bad sensor in some cases. For example, unplugging a bad IAC that is causing a surge in some models, it can change the idle, so you know the solenoid is causing trouble. And some do the same if they are having issues with the MAF. The computer uses a default setting if it doesn't receive the signal. But it's better to troubleshoot the sensor, you may have a bad connector or wire, before replacing it.

Question: If I forgot to disconnect the battery and I plugged the MAF, how I can remove the notification of the check engine?

Answer: Make sure the sensor is properly connected. Sometimes the light will reset itself. An auto parts store can check the code(s) and reset the light for you.

Question: when I connect my connector, the car shuts off. When I unplug it, it stays on but won't drive that fast. What's the problem, the connector or sensor?

Answer: Most likely, the MAF sensor is bad.

Question: I have a 2012 Chevy Malibu. It will not start. I disconnected the mass air flow sensor, now it acts like it wants to start. Could the mass airflow sensor be the problem?

Answer: It's possible. Download trouble codes and see if you get any. Faulty camshaft and crankshaft sensor produce the same symptom.

Question: What does it mean when the MAF sensor on my 1996 Chevy Tahoe has 1.23 ohms of resistance?

Answer: Reading some resistance on the signal path in the sensor means there's some "interference" against the current. This may indicate a damaged or partially burned element.

Question: Can I reuse bolts to mass air flow sensor when replacing it with a new one?

Answer: Yes you can, if they're good.

Question: On 2009 Mazda CX-7 if MAF sensor has been replaced twice with OEM part and it fails the next morning. What should I look for?

Answer: Troubleshoot the sensor and see if the sensor itself is failing. There could be a problem in the circuit, bad connector or loose wire. Also, check for a possible vacuum leak, specially between the sensor and throttle body.

Question: My check engine light is on. I cleaned the MAF sensor and reset by unplugging the battery but it came on again. The car is running normally. It continues to run even when I unplug the connection to MAF sensor. What could be wrong?

Answer: Try erasing the trouble code with a scanner tool. If the MAF sensor or its circuit is faulty, unplugging the sensor will cause the computer to run with pre-programmed parameter (estimate) until you fix or replace the sensor with a good unit.

Question: I just put a new sensor on my Lexus 2001 es300, and when I drive my car around the corner, it still dies out. What could it be?

Answer: It's hard to tell. If it only happens when turning around a corner, look for a loose wire (possibly an ignition system wire - under the dash?), or a fuel pump issue. Check for trouble codes and see if you find anything.

Question: Will my car run if the mass airflow sensor is disconnected?

Answer: It may run. If disconnecting the MAF sensor makes a possible engine problem go away, check the cam and cranks sensors and fuel pressure.

Question: I have replaced my MAF sensor three times. Last one is an AC Delco unit. Assuming that the MAF sensor is working correctly and sending information to the ECM, could the ECM be malfunctioning and causing the signal information to get distorted or misread? What else could cause outside ambient temps to be off?

Answer: There's a possibility that the ECM be malfunctioning, but is not that common. If you changed the MAF because a DTC, check the input and output voltages (incoming and outgoing) from the sensor. The problem could be in the circuit itself, the connector or a wire.

Question: I installed a new MAF sensor, but the car won't even idle. What is the cause?

Answer: If the car was idling with the old MAF sensor, disconnect the new sensor and check if the engine idles. If it does, either the new one is faulty or possibly there's something wrong with the circuit.

Question: Do I have to disconnect the battery before the MAF sensor is replaced?

Answer: No. But make sure not to leave air leaks when putting back the air cleaner assembly or you'll create a fault and cause bad engine performance.

Question: Isn’t a mass airflow sensor supposed to have a certain resistance between the signal and the ground on the sensor itself? I get about 8.8k ohm on mine. What could cause that much resistance?

Answer: It depends on your application--see your vehicle repair manual. On some models, swinging the sensor's plate flow should produce a smooth increase in resistance.

Question: I'm not getting enough voltage getting to MAF sensor. Any ideas?

Answer: If you are getting some voltage, there could be a bad connector or loose wire. Check the terminals for a loose wire or bad connection.

Question: My mass air flow sensor on an 88 Camaro 2.8 reads 5-volt reference between signal and ground while running and unplugged, on the ECM side, at idle. Shouldn't the mass air flow sensor dictate the voltage going out to the ECM? While plugged in, there is erratic non-detectable voltage, on/off, on/off. My ground tests good, and I have excellent battery voltage on ECM side of the harness. I get the same result with two mass air flow sensors.

Answer: Check the connectors and wires for loose or damage issues.

Question: When I unplug my MAF sensor, auto shakes for 1-2 seconds and then starts normally. I try to drive it with the MAF sensor and unplugged it seems to operate like normal. 2009 BMW 525I 3.0L. I have a problem when it’s cold. It has a rough starting but after 2 minutes, when it gets warmer, it’s good. What could be the problem with my car's MAF sensor?

Answer: This could be from a faulty sensor, an engine coolant temperature sensor, for example. Download trouble codes from the computer memory, even if you don't see the engine light coming on. There could be a pending code. Also, try cleaning the MAF sensor. This is a common issue. This post may help:

Question: What does it mean if, when back probing to test for voltage signal, the engine dies? Now, when turning the key to start, only power comes on and the starter does not crank. Do you have any clues to where the starter relay is located on a 1991 Park Avenue?

Answer: Check the battery connections and make sure voltage is reaching the starter relay. You may want to do a voltage drop on the starting system circuit. This other post may help:

I believe in your model the starter relay is located towards the firewall. Look to the left of the steering column. You’ll see the relay.

Question: I have an A4 Audi sedan 1.8. If I replace the airflow sensor with a new one, do I have to diagnose the car if I replace the new one with the old one again?

Answer: You might want to test the old sensor and see if it actually failed. Sometimes a clogged air filter or air leak in the ductwork can make a good MAF look bad. You can follow the procedure in the post or the one in your repair manual. It’s not a difficult procedure.

Question: My Volvo V50 runs well but then suddenly will lose power. Sometimes it helps to shake the MAF connector but not always. Is it definitely a problem with the contacts or it can be something else?

Answer: Check the sensor element for contamination and then troubleshoot it. Take a good look at the connectors and wires, possibly a loose wire that reconnects when you shake it.

Question: I have Hyundai i20 diesel 1.4 variant. Recently, the check engine light appeared in ODO meter. Then I checked it with the OBD2 tool. I got the error code P0103, which indicates MAF sensor circuit high input. What solution will work?

Answer: Test the sensor itself, its voltage output and for a poor connection. These are the most common causes for this code.

Question: When I tested my MAF sensor with a DMM it read weird. The DC voltage was set on 20, which was closest to 10. Mine would go the MAF sensor and went up to 2.49 at idle very quickly. With the engine at 2500 to 3000 rpm, it was reading 2.45 and it got to that quickly. Does that mean it's bad?

Answer: Not necessarily. Check your codes and see if it indicates problems with the circuit. If your DMM has Hz frequency - usually you'll get about 30 Hz at idle and will increase as you open the throttle.

Question: Do I have to reset my computer after replacing the mass air flow sensor and throttle body?

Answer: Not necessarily. You may want to clear the codes, and there could be a reset/relearn procedure for the ECU. Consult your vehicle repair manual. If you don't have one, your local library may have a copy.

Question: Does the power wire to the MAF have to be the same gauge?

Answer: Yes, don't use a smaller one.

Question: I am in Nigeria, and I need an AIRFLOW METER for a 1996 Nissan Maxima. Please, how can I get a good new one from a reputable part dealer?

Answer: You can contact your nearest Nissan dealer and order the part through the service department. That way you’ll be sure you are installing an OEM part.

Question: I cleaned the MAF sensor with the cleaner. It ran a little better, but still crappily. Should I replace my MAF sensor?

Answer: Double-check there are no air leaks between the MAF sensor and the throttle body. Air ducts should be properly connected and not damaged. An air or vacuum leak can confuse the computer about air volume. If possible, test the sensor before replacing it. You want to make sure you are dealing with a faulty sensor.

Question: The signal from MAF is reading 2.49-2.51v at idle and accelerating up to 2000-3000 rpm voltage, but not changing. Does this mean the MAF has failed?

Answer: Clean the sensor with MAF sensor cleaner. It's possible the sensor is dirty and messing the calibration.

Question: 1990 Mazda Miata has major take off issues. How do I go about testing the MAD on the car?

Answer: The best way is to follow the procedure in the repair manual for your particular model. You may be able to find a copy in your local auto parts store or online.

Question: P0102 engine code, rough idle, rough acceleration. Replaced mass airflow and won't idle or run. What could be the problem?

Answer: The source for the code may point to different things like the MAF circuit or electrical connector or vacuum leaks. Unplug the MAF sensor and try starting the engine. If you notice something different, the problem may be in the wiring. Check the circuit voltages using your repair manual. Also, check for a vacuum leak, including the hose between the MAF sensor and the throttle body. Hope this helps.

Question: How do you read airflow meter wires?

Answer: Use a digital multimeter and follow the instructions in the second section of this post.

Question: I got a 2006 Subaru Liberty that has no air sensor. How do I get past this?

Answer: If the sensor is missing, have it installed.

Question: How can I fix the idle air control valve?

Answer: Usually you can remove the valve and clean any buildup out of the valve and throttle body. If the valve itself is bad, replace it.

Question: Recently tested my MAF sensor and every thing looks fine. The voltage increases as the RPM increase and decreases as the RPM decreases. But when knocking on the sensor, the car struggles to idle normal or some times dies. What seems to be the problem?

Answer: There could be a broken wire in the sensor's circuitry. If lightly tapping the sensor changes the idle, the sensor is likely bad.

Question: What would cause MAF sensor output voltage go negative at times?

Answer: Sometimes this type of negative output comes from a faulty sensor; check for possible pending trouble codes (no check engine light) that might confirm this.

Question: Will a bad mass airflow sensor cause your battery to die?

Answer: No. A dead dead battery is usually caused by a faulty battery, bad alternator or circuit or a parasitic draw. This other post may help:

Question: I have a ‘98 Nissan Maxima. I replaced the coil, cam sensor, crank sensors, fuel pump, MAF sensor. What’s wrong?

Answer: Even if the check engine light is not on, download DTCs for possible pending codes. If you know you are getting good spark and proper fuel pressure, these other posts might help:

Question: 2014 Ford F150 cranks but won't start; it seems like an intermittent problem. No codes are being given. The computer was replaced and it happened again. It has been going on for the past week. I'm being advised to replace the MAF and Fuel Module Assembly. I was told it is one or the other. Any thoughts?

Answer: This type of intermittent problem usually points to electrical faults. A sensor might not be able to send the correct signal when the fault is there. Check the circuit (wires, connector, harness) for those sensors the computer depends on to manage fuel, and ignition timing. This could be the camshaft and crankshaft position sensor:

throttle position sensor:

or ignition control module.

Check the MAF sensor and circuit, if necessary:

Question: I added a new MAF to my Nissan Titan 2004. Everything came out great. The only problem I have now is that when I press the gas, the engine sounds like it is releasing air from the top. What could be the issue?

Answer: There could be a vacuum leak, but this would make the engine run rough. Make sure the air ducts are properly connected, there might be some air being sucked when the throttle opens -- sort of like a bypass.

Question: Does the Scion Xb 2008 2.4 liter have a Maf sensor fuse ?

Answer: Check under the power box lid or the fuse box inside the cabin. There should indicate the circuit fuses.