8 Symptoms of a Bad MAF Sensor, Location & Replacement Cost

Mass Air Flow Sensor

The Mass Air Flow Sensor or MAF sensor is an important part for most car engines to function properly.

It controls how much air is entering the car engine and then sends this information to the engine control unit, which controls how much fuel the fuel injectors should inject into the engine.

Unfortunately, it happens sometimes that this MAF sensor becomes worn or bad. In this article, we will talk about the symptoms of a bad MAF sensor, location, and the replacement cost.

Symptoms of a Bad MAF Sensor

  1. Check engine light
  2. A Drop in acceleration
  3. Rough or Jerky Acceleration
  4. Hard starting condition
  5. Black Smoke From Exhaust Pipe
  6. Rough idle
  7. Misfires
  8. Changed Fuel Consumption

As the mass air flow sensor is directly linked with the engine, any issue can result in disruptive performance.

Here is a more detailed list of the most common signs of a bad MAF sensor:

Check Engine Light Illuminates

Check Engine Light

The Engine control unit is full-time monitoring all the sensors in the car engine to ensure that everything is OK. If one sensor is sending a wrong signal, the ECU will light up the check engine light.

If your MAF sensor sends wrong information to the engine control unit – the check engine light will illuminate on your dashboard.

RELATED: Flashing Check Engine Light: Causes & Solutions

Drop in Acceleration

Car Acceleration

A faulty MAF sensor will cause a faulty Air-Fuel mixture. A faulty air-fuel mixture will cause a lot of strange problems with your car. A slow car is one of these things that could happen because of a faulty air-fuel mixture.

If you noticed that your car is much slower than usual, there is a significant risk that your MAF sensor is to blame.

Rough or Jerky Acceleration

Slow Car Acceleration

As you may suspect, a faulty Air-fuel mixture caused by a bad MAF sensor can also cause your acceleration to become rough or jerky.

This is most often because the air-fuel mixture becomes too lean, so the car engine is “starving” from a lack of food, and this will cause it to jerk.

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

Hard Starting Condition

Hard Starting

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

All car engines are very sensitive to the correct air-flow mixture in the exact start moment. If the air-fuel mixture is too rich or too lean at this moment, your car may not start at all or just crank a little bit longer than usual.

Black Smoke From Exhaust Pipe

Black Smoke From Exhaust

Black smoke from the exhaust is caused when the air-fuel mixture is too rich. Therefore if you realize it pours out a lot of black smoke from your exhaust pipe – there is a considerable risk that your engine is running too rich, which a bad MAF sensor can cause.

You can also notice a gray-colored smoke, but much more smoke than usually if your engine is just running slighter richer than usual.

Rough Idle

Low Idle Rpm

The engine’s most sensitive situation to engine problems is at idle. This is also why you most often notice problems with the air-flow or ignition on idle.

If your idle has become very tough lately or if it is even stalling – there is a big chance that your MAF sensor has gone bad.

RELATED: Rough Idle Causes & How to Fix it

Misfires

Car Misfire Spark Plugs

Misfires happen when one or more cylinder fails to combust the fuel. To combust the fuel correctly, the engine needs 3 things – the right air-fuel mixture, an ignite, and compression.

Therefore if the air-fuel mixture very far out of the specifications, it may cause one or more cylinders not to fire up at all, and this will cause the engine to misfire.

Changed Fuel Consumption

High Fuel Consumption

This last symptom is probably the most obvious as you already know that a faulty MAF sensor causes a wrong air-fuel mixture. Therefore a faulty MAF sensor can cause the fuel consumption to either going up or down.

You may think that the fuel consumption going down is a good thing – but it might actually damage your engine, which will cause it to become more expensive in the future.

MAF Sensor Location

Maf Sensor Location

The MAF sensor is located on the big hose between the intake manifold and the air filter box, often installed on the air filter box.

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

You can use a repair manual to ensure the location or use the internet for a quick search. Check the pictures for a clue as to where it can be located.

Diagnosing a Failing Mass Air Flow Sensor

Diagnose Maf Sensor

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

Diagnosing a MAF sensor is often relatively easy if you know what you are looking for. However, to properly diagnose the MAF sensor, you need to correctly measure values for your specific car engine and model, which you can find in a repair manual.

  1. Connect an OBD2 scanner and check the live data from the MAF 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 to the MAF sensor and check for corrosion.
  4. Check your repair manual to measure the sensor and the wirings to it. You can find out more about how to test the MAF sensor in this video.
  5. Clean or Replace the MAF sensor if faulty or repair the wirings if faulty.

Cleaning a Dirty MAF Sensor

Often, the problems associated with the mass air flow sensor occur due to dirt and debris buildup on the sensor head. This particle accumulation over time results in poor performance of the sensor.

Cleaning the MAF sensor is often relatively straightforward. Just remove the sensor head from the MAF sensor housing and carefully clean the sensor head with an electronic cleaner or a specific sensor cleaner like this one:

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MAF Sensor Replacement Cost

The average MAF sensor replacement cost is between 140$ to 550$, depending on the car model and labor costs. A Mass Air Flow Sensor costs 100-400$ while the labor costs 40$ to 150$.

The MAF sensor itself is often quite expensive, as you sometimes have to replace the whole MAF sensor housing. Even the sensor itself can be expensive.

Luckily, replacing the MAF sensor is often very easy and done in 10 minutes for most car models. You can often do this yourself if you just have basic car skills.

MAF Sensor FAQ

How do you know if you have a bad mass air flow sensor?

There is a lot of signs that signals that you MAF sensor has gone bad. One of these signs are a check engine light, lower engine performance, rough idle and changed fuel consumption.

What happens when MAF sensor goes bad?

The MAF sensor is a vital part of the car engine, and therefore a lot of things can happen with your car engine when it goes bad. The most common things that happen are a check engine light, bad engine performance, rough idle, 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 the resistance you should see on the multimeter, you can check in your repair manual for your car model.

Can you drive with a bad mass air flow sensor?

A bad mass air flow sensor may cause a lot of problems with your car engine, and therefore it is not recommended to drive with it. If your engine is running fine, you can drive slowly to the closest repair workshop without problems, though.

Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.