8 Symptoms of a Bad MAF Sensor (& Replacement Cost)
The Mass Air Flow Sensor or MAF sensor measures the air entering the engine to calculate the correct air-fuel mixture. Here’s how to tell if you have a bad MAF sensor
- By Magnus Sellén
- Updated: September 5, 2022
The Mass Air Flow Sensor (MAF) is an important part for car engines to function properly. It measures how much air enters the car engine and then sends this information to the engine control module, which then controls how much fuel the fuel injectors should inject into the engine.
Unfortunately, it sometimes happens that the MAF sensor gets worn or bad. In this article, we will talk about the symptoms of a bad MAF sensor, location, and replacement cost.
8 Bad MAF Sensor Symptoms
The most common symptoms of a bad mass airflow sensor are a check engine light on your dashboard and engine performance issues.
The main symptoms of a bad or failing MAF sensor include:
Because the mass airflow sensor is directly connected to the engine control system, any problem can interfere with performance. Here is a more detailed list of the most common symptoms of a bad mass air flow sensor:
Check Engine Light Illuminates
The engine control module 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 engine control module does not always recognize a faulty MAF sensor, so it may still be defective even if there is no engine light on your dashboard. But, if your check engine light is illuminating you want to check the diagnostic trouble codes first with an OBD2 scanner.
Your engine needs a perfect air-fuel mixture in the combustion chamber for optimal performance. 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.
If you notice that your car is much slower than usual, there is a significant risk that your MAF sensor is at fault.
Hesitation, rough 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.
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 air mass 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.
Black Smoke From Exhaust Pipe
Black smoke from the exhaust pipe 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.
You can also notice a little more gray smoke from the exhaust pipe than usual if your engine runs rich. This can also damage your catalytic converter, which is very expensive so you definitely want to fix it as soon as possible.
The car engines’ most sensitive situation for engine problems is at idle and during the starting moment. Therefore, it is very likely that problems will occur at idle also.
If your idle has become very rough lately or if the engine is stalling – there is a big risk that your MAF sensor has gone bad.
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.
Changed Fuel Consumption
This last symptom is probably the most obvious because you already know that a faulty MAF sensor is causing a faulty air-fuel mixture. Therefore, a faulty MAF sensor can cause fuel consumption to either go up or down.
You may think that reduced fuel consumption is a good thing – but it can actually damage your engine, which will make it more expensive in the long run.
MAF Sensor Location
The MAF sensor is located on the large 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 design.
You can use a repair manual to find the exact location or use the internet for a quick search. Check out the pictures for a clue as to where it can be placed.
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’s hot wire with an electronic cleaner or a specific MAF sensor cleaner like this one:
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However, the sensor’s hot wire is very sensitive and you can easily damage it therefore you don’t want to touch it with your hands or with a towel! Just spray it and let it dry, it should be enough!
Diagnosing a Failing 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. But to diagnose the MAF sensor correctly, you must have correctly measured values for your specific car engine and model, which you can find in a repair manual.
- Connect an OBD2 scanner and check the live data from the MAF sensor on idle. It should be 0 mg.
- 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.
- Remove the plug to the MAF sensor and check for corrosion.
- 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.
- Clean or Replace the MAF sensor if faulty or repair the wirings.
MAF Sensor Replacement Cost
The average MAF sensor replacement cost is between $140 and $550, depending on the car model and labor costs. A Mass Air Flow Sensor costs $100 and $400 and you can expect the labor costs to be $40 to $150.
The MAF sensor is often quite expensive, as you sometimes have to replace the whole MAF sensor housing also, but even just the sensor itself can be quite expensive.
Fortunately, it is often very easy to replace the MAF sensor and is done in 10 minutes for most car models. You can often do this yourself if you only have basic car knowledge.
MAF Sensor FAQs
What happens when the MAF sensor goes bad?
The MAF sensor is a vital part of the car engine, and therefore a lot of 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 you drive with a bad mass air flow sensor?
A bad air mass sensor can cause many problems with your car engine, and therefore it is not recommended to drive with it. However, if your engine is running well, you can drive slowly to the nearest workshop.
How often does a mass air flow sensor need to be replaced?
There is no service schedule for when to replace the MAF sensor. The MAF sensor is made to last the life of the vehicle, so it should only be replaced if it is faulty. However, you can clean the MAF sensor every 100,000 miles to keep it functional.