How to Test a MAF Sensor

Updated on August 5, 2019
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Test your MAF sensor before replacing it.
Test your MAF sensor before replacing it. | Source

Symptoms of a Bad Mass Air Flow Sensor

Symptoms of a faulty mass air flow (MAF) sensor may include:

  • poor fuel economy
  • erratic performance
  • hesitation
  • hard starting
  • no starting
  • stalling when put gear engaged
  • low engine power
  • engine running in fail-safe mode

What a MAF Sensor Does

The MAF sensor measures the volume and density of the air entering the engine. Some also measure the temperature of the air entering the engine. The computer uses this measurement, along with other inputs, to calculate the best air-fuel ratio and spark timing according to engine operating conditions. On a car with an automatic transmission, the MAF sensor may help with shift timing as well.

Although there are two common types of MAF sensors, hot-wire and hot-film, hot-wire types are the most common. Troubleshooting test procedures for hot-wire sensors may vary from one vehicle make to the next. You can further divide MAF sensors into low-frequency, voltage, and high frequency types.

Some vehicle models use a MAF sensor that communicates with a voltage signal to the computer. But more recent models may use a voltage frequency signal.

What You Need to Troubleshoot Your MAF Sensor

Whatever your sensor type, general troubleshooting steps remain basically the same. If you have a decent digital multimeter (DMM), you should be able to test your MAF sensor on most vehicles. In some cases, though, you’ll need a DMM meter with a frequency scale.

Whatever the case, it’s a good idea to have the vehicle repair manual for your particular model to check the correct specifications and type of sensor your vehicle is using. If you don’t have this manual, you can buy one from Amazon. Haynes manuals come with step-by-step procedures for many troubleshooting, replacement and maintenance projects you can do at home.

The following are general testing procedures that can apply to most vehicle models on the road today.

Location of the MAF Sensor

Look for the MAF sensor between the air filter box and the throttle body. On some models, the sensor is inside the air filter housing.

If you need help locating the sensor, get the vehicle repair manual for your particular vehicle make and model.

Index
1. A Quick MAF Sensor Diagnostic Procedure Without a DMM
2. How to Test a MAF Sensor
Testing the MAF sensor’s power feed
Testing a MAF sensor’s voltage signal
Testing a MAF sensor’s frequency signal
Testing the MAF sensor’s hot wire
3. I Replaced My Bad MAF Sensor But I See No Improvement
4. What If My MAF Sensor is Good
Look for the MAF sensor in the air cleaner assembly.
Look for the MAF sensor in the air cleaner assembly. | Source

1. A Quick MAF Sensor Diagnostic Procedure Without a DMM

Sometimes, it’s possible to do a quick diagnostic of the MAF sensor without the use of any test equipment, depending on the particular sensor fault. For example you can try this when dealing with intermittent performance issues, a no-start condition or poor idle problems.

If your vehicle has been experiencing intermittent faults or poor idle problems:

  1. Engage the parking brake.

  2. Set the transmission to Park (automatic) or Neutral (manual).

  3. Start the engine and let it idle.

  4. Pop the hood open.

  5. Lightly tap the MAF sensor with a screwdriver handle.

    • If the engine stalls, idle is upset, or idle gets better, the MAF sensor is likely defective.

If the engine doesn’t start or idles poorly:

  1. Pop the hood open.

  2. Unplug the MAF sensor electrical connector.

  3. Engage the parking brake.

  4. Set the transmission to Park (automatic) or Neutral (manual).

  5. Try starting the enigne.

    • If the engine starts or idle improves, replace the MAF sensor.

On some vehicle models, you need to use a DMM capable of reading frequency.
On some vehicle models, you need to use a DMM capable of reading frequency. | Source

2. How to Test a MAF Sensor

Generally, there are three types of MAF sensors that have been used over the years: low frequency, DC voltage, and high frequency type.

For example, GM used low-frequency type MAF sensors in 1988 and older models. Then it switched to high-frequency sensors starting in 1989. Most newer vehicle models use high frequency type sensors as well.

When performing these tests, try checking for a voltage signal; if you know your MAF sensor is a high-frequency type (newer vehicle model), you can use a voltmeter capable of measuring frequency. If you have an old vehicle model with a low-frequency type MAF sensor, you can use a digital multimeter that is able to measure vehicle speed (tachometer, rpm). If necessary, consult your vehicle repair manual.

If possible, start the engine and let it idle for about 15 minutes to warm it up. Then shut off the engine and continue with the following tests.

Testing the MAF sensor’s power feed:

  1. Pop the hood open.
  2. Unplug the MAF sensor electrical connector.
  3. Set your DMM to 20 volts DC or autorange.
  4. Connect your meter’s red lead to the B+ terminal on the harness connector (the one leading to the computer). Consult your vehicle repair manual to identify wires, if necessary.
  5. Connect your meter’s black lead to the ground (-) pin on the sensor connector.
  6. Turn the ignition switch to the On position, but don’t start the engine.
  7. You should get over 10 volts or pretty close to battery voltage; otherwise, there’s a problem in the power side of the circuit.

Testing a MAF sensor’s voltage signal:

  1. Turn the ignition switch to the Off position.

  2. Plug in the MAF sensor’s electrical connector.

  3. Backprobe the sensor’s signal (+) wire with your meter’s red lead, and the ground (-) wire with your meter’s black lead.

  4. Make sure the meter’s leads are away from moving engine components.

  5. Engage the parking brake and set your transmission to Park (automatic) or Neutral (manual).

  6. Start the engine and let it idle.

  7. Your meter should register 0.5 to 0.7 volts. On some models, this initial voltage at idle may be higher.

  8. Lightly tap the MAF sensor with the handle of a screwdriver or wrench.

    • Voltage output should remain steady.
    • If it fluctuates or the engine misfires or surges, there could be loose electrical connections inside the sensor and needs to be replaced.
  9. Increase engine speed between 2500 and 3500 rpm.

  10. The sensor’s output signal should increase smoothly between 1.5 and 3.0 volts.

    • If the reading becomes erratic or output voltage seems slow, the hot-wire or sensing element may be dirty or contaminated. If dirt or contamination is the problem, this may suggest a bad self-cleaning circuit or relay.
    • If there’s no output response from the sensor, replace it.

The next video shows you how to quickly test your MAF sensor using a multimeter.

Output signals from a hot-wire (red) and hot-film (black) type MAF sensors.
Output signals from a hot-wire (red) and hot-film (black) type MAF sensors. | Source

Testing a MAF sensor’s frequency signal:

  1. Turn the ignition switch to the Off position.

  2. Plug in the MAF sensor’s electrical connector

  3. Set your DMM to the Frequency scale. See your meter user’s manual, if necessary, to connect the red lead to the correct jack on your meter.

  4. Backprobe the sensor’s signal (+) wire with your meter’s red lead, and the ground (-) wire with your meter’s black lead.

  5. Make sure the meter’s leads are away from moving engine components.

  6. Engage the parking brake and set your transmission to Park (automatic) or Neutral (manual).

  7. Start the engine and let it idle.

  8. The MAF sensor’s output should be about 30 hertz (Hz). Consult your vehicle repair manual for the correct specification for your particular vehicle model.

  9. Lightly tap the MAF sensor with the handle of a screwdriver or wrench.

    • Frequency should remain steady.
    • If it fluctuates or the engine misfires or surges, there could be loose electrical connections inside the sensor and needs to be replaced.
  10. Ask an assistant to gradually increase engine speed by depressing the accelerator pedal.

  11. The sensor’s output frequency should increase smoothly as well. Consult your vehicle repair manual, if necessary.

    • If the Frequency becomes erratic or seems slow, the hot-wire or sensing element may be dirty or contaminated. Also, the problem may point to a bad self-cleaning circuit or relay.
    • If there’s no output response from the sensor, replace it.

Set your DMM meter to Ohms to measure test the MAF's hot-wire.
Set your DMM meter to Ohms to measure test the MAF's hot-wire. | Source

Testing the MAF sensor’s hot wire:

Sometimes, a MAF sensor’s hot wire breaks or gets damaged. This test will help you check the condition of this wire.

  1. Turn the ignition switch to the Off position.
  2. Unplug the MAF sensor’s electrical connector.
  3. Set your DMM to the Ohms scale.
  4. Connect your meter leads to the signal (+) and ground (-) pins on the sensor connector. Consult your vehicle repair manual, if necessary.
  5. If the sensor’s hot wire is damaged, your meter will register infinite resistance.

When replacing the MAF sensor, install the correct replacement for your application.
When replacing the MAF sensor, install the correct replacement for your application. | Source

3. I Replaced My Bad MAF Sensor But I See No Improvement

If your MAF sensor didn’t pass the tests, you’ll need to replace the sensor. Still, be aware of this recommendations and potential problems after installing the new sensor.

  • Make sure to install the correct sensor for your particular application.
  • If there are any trouble codes pointing to the MAF sensor, make sure to clear them from the computer’s memory.
  • Your engine may idle or run a bit rough after installing a new sensor. Give some time to other sensors and actuators to readjust.
  • If possible, replace the air filter and thoroughly clean the air cleaner assembly.
  • Make sure the air cleaner assembly is properly connected and there are no air leaks.

Even a dirty air filter can cause the MAF sensor to send a faulty signal.
Even a dirty air filter can cause the MAF sensor to send a faulty signal. | Source

4. What If My MAF Sensor is Good?

There are several potential faults that can trigger a trouble code for an otherwise good MAF sensor. And this can be confusing if you decide to replace components without any testing first.

Here are some pointers that may help you when the MAF sensor tests good:

  • Debris or dust that interfere with the hot-wire or sensing element on a MAF sensor can also trigger a P0101, P0102, or P0103 trouble code.
  • If you find the hot-wire element dirty, you may want to check the self-cleaning circuit and relay for a possible fault. Consult your vehicle repair manual.
  • Make a visual inspection of the sensor wires and harness connector for contamination, loose or damaged wires.
  • Check the air filter for clogging, filter housing and ductwork for debris and dust.
  • The air cleaner assembly and hoses should be properly connected and tight to avoid air leaks. The large clamps should hold hoses in place and tight.
  • Check the throttle plate and bore for dirt and carbon buildup.

Other potential problems that may trigger a MAF sensor trouble code on some particular models:

  • Loose oil fill cap
  • Sticking EGR valve
  • Leaking crankcase ventilation breather pipe
  • Dipstick not properly seating

Other potential faults can trigger a P0101 MAF-sensor-related fault:

  • Leaking air intake boot
  • Vacuum leak
  • Clogged or not properly installed air filter
  • Clogged catalytic converter

Also, keep in mind that a MAF sensor may develop minor problems that can’t be detected with a regular voltmeter. In this case, you need a professional scan tool or other sensitive testing equipment to detect slight variations in sensor operation.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

    © 2019 Dan Ferrell

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