What is MAF Sensor? | Symptoms of bad Mass Air Flow Sensor

The mass air flow (MAF) sensor is an integral part of most car engines to run properly. The MAF sensor measures how much air enters the car engine and sends this information to the engine control module (ECM), which controls how much fuel the fuel injectors should inject. This article explains the MAF sensor working, symptoms, and causes.

What is MAF Sensor?

The Mass Air Flow sensor or MAF sensor is used to determine the mass flow rate of air entering the internal combustion engine to calculate the correct air-fuel mixture.

MAF Sensor

The air mass information is necessary for the engine control module (ECM) to balance and deliver the correct fuel mass to the engine. Air changes its density with temperature and pressure.

In automotive applications, air density varies with the ambient temperature, altitude, and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder.

When a vehicle’s mass air flow sensor is faulty or defective, it can cause various problems and usually results in poor performance from your engine.

When a MAF sensor is used in conjunction with an oxygen sensor, the engine’s air/fuel ratio can be controlled very accurately. The MAF sensor provides the open-loop controller predicted air flow information (the measured air flow) to the ECM/PCM, and the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass.

Working of MAF Sensor

MAF sensor is located between the air filter and the throttle body. It is responsible for measuring the amount of air entering the engine. The MAF sensor works on the work on the hot wire principle.

Working of MAF Sensor

Most vehicles have hot wire MAF sensors. This sensor has one heated wire and one ambient temperature wire.

One wire is heated by an electrical current, and the other is not. As air flows across the heated wire, it cools down.

When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or voltage sent to the ECM and interpreted as air flow. The quantity of air entering the engine is adjusted accordingly.

The ECM then controls the injectors to deliver the specific amount of fuel that’s proportional to the airflow, creating an air-fuel mixture that, ideally, is perfect for your engine.

Symptoms of a bad MAF Sensor

A faulty mass air flow sensor will cause problems similar to low compression or low vacuum and will also show symptoms similar to when your vehicle has low fuel pressure from a faulty fuel pump.

As the MAF sensor goes bad, it produces one of the below-given symptoms:

  1. Misfires
  2. Hard starting condition
  3. Rough idle
  4. Trouble
  5. Accelerating
  6. Poor fuel economy
  7. Hesitation or jerky acceleration
  8. Black Smoke from Tailpipe
  9. Check Engine Light Illumination

1) Misfires

Misfires occur when one or more cylinders fail to burn the fuel. To burn the fuel correctly, the engine needs 3 things – the right air-fuel ratio, ignition, and compression.

Therefore, if the air-fuel mixture is very far beyond the specifications, it may cause one or more cylinders not to ignite at all, and this will cause the engine to ignite incorrectly, causing a misfire. If you find any trouble codes related to misfires, it can be a sign of a bad mass air flow sensor.

2) Hard Starting Condition

If you notice that your car has become more difficult to start in the morning, there is a chance that a bad MAF sensor is causing the problem.

All car engines are very sensitive to the right airflow mixture at the exact starting moment. If the wrong amount of fuel is injected into the engine at the moment, your car may not start at all or just crank a little longer than usual.

3) Rough Idle

Smooth idle is difficult to achieve without the proper amount of fuel. If the mass air flow sensor has issues, the engine may not run smoothly, especially while idling.

4) Trouble Accelerating

Slow or problematic acceleration is one of the most common symptoms of a bad MAF sensor.

For optimal performance, your engine needs a perfect air-fuel mixture in the combustion chamber. A faulty MAF sensor can cause a faulty air-fuel mixture, and it can cause many strange performance issues with your car, and slow acceleration is one of them.

5) Poor Fuel Economy

As the MAF sensor goes bad, it doesn’t send the correct signal to ECM. If the ECM errs rich, it may add more fuel than necessary, causing poor fuel economy.

6) Hesitation or jerky acceleration

As you may suspect, a faulty fuel injection caused by a poor MAF sensor can also make your acceleration rough or jerky.

This is usually because the air-fuel mixture becomes too lean, so the car engine “starves” due to lack of food, and this will cause it to jerk.

If the air-fuel mixture is too rich, it can also extinguish the ignition created by the spark plug, which causes the acceleration to be rough.

7) Black Smoke from Tailpipe

Black smoke from the tailpipe is a strong sign that your engine is getting too much amount of fuel compared to the amount of air. Therefore, if you realize that a lot of black smoke is pouring out of your exhaust pipe – there is a significant risk that your engine runs too rich, which a bad MAF sensor could cause.

If your engine runs rich, you can also notice a little more gray smoke from the exhaust pipe than usual. This can also damage your catalytic converter, which is very expensive, so you definitely want to fix it as soon as possible.

8) Check Engine Light Illumination

The engine control module (ECM) monitors all sensors in the car engine to ensure that everything is OK. If a sensor sends an incorrect signal, the ECM or PCM will turn on the check engine indicator light.

Therefore, if your MAF sensor is faulty and sends wrong information to the engine control unit – the check engine light will illuminate your dashboard.

However, the ECM does not always recognize a faulty MAF sensor, so it may still be defective even if there is no engine light on your dashboard.

Read More: Causes of Check Engine Light Illumination

MAF Sensor Location

The mass air flow sensor (MAF) is a key component of the electronic fuel injection system in a car. It is located between the air filter and the engine’s intake manifold.

Its exact location varies from manufacturer to manufacturer, as they fit the sensor based on the engine design.

You can use a repair manual to find the exact location or use the internet for a quick search. 

How to Diagnose a bad Mass Air Flow Sensor?

MAF sensors can often be quite expensive, and therefore it is important to make a correct diagnosis before choosing to replace the MAF sensor.

Diagnosing a MAF sensor is often relatively easy if you know what to look for. Follow the below-given steps to diagnose the MAF sensor:

  1. Connect an OBD2 scanner and check the live data from the mass air flow sensor on idle. It should be 0 mg.
  2. Start the car and check the values from the MAF sensor again. It should go up when you rev the engine and down as the engine RPM decreases; if the value is stable, there is either something wrong with your diagnostic tool, MAF sensor, or the wirings to it.
  3. Remove the plug from the MAF sensor and check for corrosion.
  4. Check your repair manual to measure the sensor and the wirings to it.
  5. Clean or replace the sensor if needed.
  6. Allow 20 minutes for the sensor to sit after cleaning it with either the cleaner or alcohol, then reinstall it in your car. Before it can be replaced in your vehicle, the sensor must be completely dry; otherwise, you risk damaging it.

 MAF Sensor Replacement Cost

The replacement cost of the Mass Air Flow Sensor varies according to the labor cost, vehicle model, and type of brand. The average replacement cost of the MAF sensor is from $130 to $560. In this cost, the labor costs are from $35 to $160, while the sensor cost is from $95 to $400.

Common Fault Codes

Common fault codes and causes include:

  • P0104: MAF circuit intermittent
  • P0103: MAF circuit high input
  • P0102: MAF circuit low input
  • P0101: MAF circuit range/performance
  • P0100: MAF circuit malfunction
  • P0171system too lean (bank 1) and P0174 system too lean (bank 2) are also often caused by a faulty or contaminated MAF sensor.

FAQ Section

What does a MAF sensor do?

A mass air flow sensor calculates the oxygen flowing to your engine for the ideal air-to-fuel ratio. The mass airflow sensor helps to increase engine efficiency by doing so. Most cars use the hot wire principle when it comes to the airflow sensor.

How often do MAF sensors go bad?

The MAF sensor needs to be replaced every 10,000 – 12,000 miles. Your MAF sensor’s life can be extended with regular maintenance and air filter replacement. A good rule of thumb is to go by the book every 10,000 to 12,000 miles. There is no such thing as an expiration date for a mass airflow sensor (MAF).

Can I drive with the MAF sensor unplugged?

While unplugging the MAF sensor to test whether it’s the cause of your problems is fine, you should not continue driving without it. The limp mode is not optimal for long-term driving, and your engine needs the MAF sensor to run properly.

Can a bad MAF sensor cause misfire?

A bad or dirty MAF sensor can cause a lean code and/or misfire to occur. The engine may be stalling because it isn’t getting enough throttle openings.

How to clean a MAF Sensor?

  1. Unplug the Sensor: Turn the engine off, remove the keys from the ignition, and let the engine cool. Locate the mass air flow sensor by consulting your owner’s manual. Unplug the part from the vehicle’s electrical system.
  2. Remove the Sensor: With the sensor unplugged, loosen the clamps and any brackets holding it in place. Slide the sensor assembly away from the tubing and carefully remove it from the air intake boot(s).
  3. Clean the Sensor: Place the sensor on a towel for cleaning. Apply the cleaner — 10-15 blasts around the inside of the sensor will do.
  4. Reinstall the Sensor: Allow the sensor to dry. This should only take a few seconds. Once the part is ready, you can re-install it back into place, reattach and tighten the clamps/brackets.

What happens when the Mass Air Flow sensor goes bad?

The mass air flow sensor is a vital part of the car engine; therefore, many things can happen to your car engine when it gets bad. The most common things that happen are a control lamp, poor engine performance, uneven idling, and changed fuel consumption.

How do you test a MAF sensor?

To test a MAF sensor, you need a multimeter to measure the resistance in the sensor. To know which resistance you should see on the multimeter, you can look it up in your repair manual for your car model.

Can I drive with a bad MAF sensor?

Yes! It is possible to drive with the signs of a bad MAF sensor but for a specific duration. However, driving with a bad MAF sensor is not recommended to lead the driver towards engine issues.

Can a mass air flow sensor mess up your transmission?

A failing air flow sensor can cause a variety of driveability issues, including a no-start, stalling, power loss, and sluggish acceleration. A malfunctioning air flow sensor may also affect the automated gearbox’s shifting pattern.

What is the lifespan of a mass air flow sensor?

Mass air flow sensors are designed to last the lifetime of your vehicle. In fact, they have no scheduled replacement interval. For this reason, the sensor is generally not replaced until it fails.

Does cleaning a MAF sensor work?

If the MAF sensor is at fault, cleaning it can help, and many times, even solve the problem. This can be done at home. You just need to remove the component, clean it, and reattach it to your engine air intake system.

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