Why Replaced MAF Sensor Check Engine Still On [Reasons + Solutions]

The main reasons behind a replaced MAF sensor check engine still on are not replacing it properly, not resetting the ECU, clogged air filter, leaking intake manifold gasket, and vacuum leak.

You can solve this problem by reinstalling the MAF sensor correctly or by resetting the ECU in most cases. You can learn how to do these things in detail by following this guide.

We’ll also discuss the other reasons that cause this issue and how you can go about getting rid of the CEL. You’ll also learn the signs of a bad MAF sensor and how you can trick it. Let’s dive in!

Why Replaced MAF Sensor Check Engine Still On [Reasons + Solutions]

It’s fairly common to see the check engine light come on because of a faulty mass airflow sensor. But when the issue still remains after replacing it, it can be difficult to understand the causes behind it. We’ll take a look at why it happens in this section.

Note: You can also read why replaced MAF sensor is still rough idle and how to fix it.

1. Not Replacing It Properly

Many people would go to extreme lengths to save a couple of bucks. And there’s nothing wrong with that as long as you know what you’re doing.

But if you try to replace a MAF sensor without a proper guideline or previous experience, you may have made a mistake somewhere.

not replacing it properly

If you made any errors while installing the new sensor, it could be the reason why the check engine light is not going off.

A sign of making this mistake is that your car runs worse with a new MAF sensor instead of better performance.


Luckily, this problem is an easy one to fix. You can take it to a local mechanic and he’ll be able to install the new MAF sensor correctly. But if you’re keen on doing it the right way yourself, you can follow these steps:

  • Locate the MAF sensor in your car.
  • Disconnect both the negative and positive terminals of the battery.
  • Squeeze the connectors attached to it.
  • Unscrew it using a Philips screwdriver and pull it out.
  • Place the new MAF sensor where the old one used to be.
  • Tighten the screw and attach it to the connectors.

That’s how you can replace the sensor correctly. It’s a good idea to change the air filter as well when you’re replacing the MAF sensor to prevent air with dirt from clogging it. Good quality air filters will make it last longer as well.

Before replacing the sensor, it’s a good idea to clean it and see if you can get the check engine light to come off. Just take it out and spray it with some MAF sensor cleaner. Let it dry for about half an hour and put it back on.

Whether you’ve cleaned or replaced the MAF sensor, it’s important to erase the error codes so that you can get rid of the check engine light.

Now, you can replace it the correct way even if you do it on your own. If the CEL doesn’t come on anymore, you’ve fixed your problem.

2. Not Resetting The ECU

Do you have to reset ECU after changing the MAF sensor? Yes, you must do it if a bad MAF sensor was causing the check engine light to come on and you want it to turn off.

If you don’t reset it, your car will have no idea that you’ve changed the sensor and the CEL will still be on.


Replacing the sensor itself doesn’t mean that the job is complete. So, what to do after replacing the mass air flow sensor? There are many ways you can go about resetting it so that the check engine light turns off.

The easiest way to reset the ECU is to disconnect the battery for 15-30 minutes. After replacing the MAF sensor, make sure the engine is turned off and cool before disconnecting the battery terminals.

If you leave it overnight, there are no issues. The longer it doesn’t have any connection to the battery, the more the ECU will have to relearn stuff. After resetting the ECU this way, the check engine light should go off.

You can also just keep driving your car if you don’t want to reset the ECU. The check engine light will be on at first but after a few weeks of driving, it’ll most likely be turned off on its own.

That’s because the ECU will automatically learn the parameters of the new MAF sensor with time.

3. Clogged Air Filter

When your check engine light indicates a bad MAF sensor, it usually means that your engine isn’t getting proper airflow.

Now, it’s not necessary that the problem lies with the MAF sensor. You may have replaced it thinking that it was causing the issue.

clogged air filter

But a clogged air filter is also a common culprit behind this issue. If you have a scan tool and you get a P0102 error code, you can confirm that the amount of air traveling through the air filter is lower than what it’s supposed to be.

Even if you have other error codes, the issue could lie with the air filter. If you inspect it visually, you’d also be easily able to tell if it’s clogged.

The check engine light will come on in such cases and won’t go off even after replacing the MAF sensor as it wasn’t causing the issue here in the first place.


Replacing an air filter is thankfully an easy and inexpensive job. You can find it in any auto shop and replace it yourself. When you’re getting an air filter, make sure you get high-quality one.

If you just get your hands on the cheapest one you can find, the fibers can get sucked into the engine, and it can go into the airflow meter. It’ll be ruined when the airflow meter gets too hot.

Think of the air filters as an investment rather than an expense. If you use good ones, it’ll make the other components in your engine last longer including the MAF sensor.

4. Leaking Intake Manifold Gasket

The intake manifold in your car makes sure that the air coming into your car’s engine is evenly distributed to all the cylinders to start and continue the ignition process.

It also keeps the engine cool as the coolant flows through it. The intake manifold gasket also does an important job.

intake manifold gasket

It makes sure the ignition and the cooling processes go well by providing a seal and not letting any air on coolant escape through it. But these rubber gaskets are bound to fail with time and cause leaks.

When that happens, there’ll be bad airflow, and the check engine light can be triggered showing a bad MAF sensor.


If a bad intake manifold gasket is causing the issue in your case, you’re lucky as it’s a super easy and cheap fix.

You can find a rubber gasket for less than $10 and replace the old one. It’ll usually last for five years or so if you take good care of it.

5. Vacuum Leak

The entire air intake system of your car needs to be sealed to ensure proper airflow and regulate the temperature. The intake manifold gasket isn’t the only culprit that can cause leaks.

testing a vacuum leak

Any leaks in the rubber hoses or the air ducts can result in extra air in your engine that won’t be registered by the MAF sensor.

The check engine light will be triggered signaling a bad MAF and it won’t go away even when you replace it with a new one.


If you’re dealing with a vacuum leak, it can be an easy or difficult problem to fix depending on its source. You can test for vacuum leaks coming from the hoses by having a mechanic do a smoke test on them. If you detect one, you need to fix it.

As far as cracks in air ducts are concerned, you would be able to hear whistling noises coming from them or visually see the damage.

You can cover up the leak with a sealant if it’s a small leak. Otherwise, you’d have to replace the damaged section. You can do it yourself or hire a mechanic for this job.

What Are Signs Of A Bad MAF Sensor

As you already know, just relying on the signal of the check engine light and changing the MAF sensor isn’t the right approach.

It can be a false alarm when in reality, the issue lies with another component. So, how can you tell when it’s actually the MAF sensor that’s bad?

There’s no way to do it for sure. Even if you see codes like P0101 or P0102 which indicate MAF sensor issues, it’s still possible that the sensor isn’t at fault here.

So, you need to be on the lookout for some common signs to know when should MAF sensor be replaced. Here are the most common ones:

i). Hesitating During Acceleration

If you notice hesitation or a sudden jolt of power when you’re trying to speed up your vehicle, that’s the first sign of a bad MAF sensor. Driving a car in this condition can be dangerous So, you shouldn’t ignore this signal if you see it happening to you.

ii). Rough Idling

Will a bad MAF sensor cause rough idle? There are many things that can cause a rough idling issue in your car.

Some of them are faulty spark plugs, dirty fuel injectors, clogged fuel filters, and a bad fuel pump. But, it can also happen due to a bad MAF sensor. Look into it if there are no issues with the spark plugs.

iii). Engine Misfiring

When the MAF sensor goes bad, it can send the ECU wrong signals about the amount of air present in the engine. The fuel injectors will inject less or more fuel depending on that reading and that can cause the engine to misfire and stall frequently.

iv). Trouble Starting The Engine

As the mixture of air and fuel will be off when you have a bad MAF sensor, you’ll often have difficulty starting the engine.

Your car will also need more fuel if extra air goes into the air intake system and you’ll also notice poor fuel efficiency when you have a bad MAF sensor.

v). Black Smoke From Exhaust Pipes

If you see any black smoke coming out of the exhaust pipes, it means that the engine is running too rich. The engine either has too much fuel or too little air. This miscalculation is often the result of a faulty MAF sensor.

How To Trick A Mass Air Flow Sensor

Before you learn how to trick the MAF sensor, remember it’s there for a reason. We don’t recommend trying to trick it for your safety.

But there can be some urgent situations where you have no other option except to do it. With that in mind, let’s learn how you can achieve it.

You’ll need to make a tube similar to the shape and size of the mass airflow sensor in your car in order to trick it.

The main difference between the original and this one is that while the original will be made with plastic, the tube will be made with metal.

Place the tube in front of your car’s ignition source so that it can heat up the MAF sensor to the same temperature as the air-fuel mixture in your car.

Keep in mind that the heat from an open flame can trick the MAF sensor to measure higher readings than it should. It can be harmful to your engine.


How can you tell if the MAF sensor is bad?

Your car running poorly, rough idling, black smoke coming out of your exhaust pipes, and the check engine light coming on are all signs that your MAF sensor is bad and needs replacement.

Should you disconnect the battery when changing the MAF sensor?

It’s a good idea to disconnect it when you’re replacing a MAF sensor as it’ll make sure that no electricity flows from the ground to the electrical cables in your car. It’ll prevent an accident and make the replacement safer.

Why does a MAF sensor fail?

The most common reasons behind a failing MAF sensor are contact issues at the electrical connections, mechanical damage from vibration during driving, and measuring element drifting.

What turns on the check engine light after unplugging MAF?

The CEL can come on if you unplug the MAF sensor with the engine on as the ECU will detect component failure. If you drive for a few weeks, it’ll disappear but the error codes will remain unless you get them cleared.


When you see the check engine light come on displaying the MAF sensor, you think replacing it will do the trick. So, it can be frustrating when you see that replaced MAF sensor check engine still problem prevails for your engine.

Hopefully, now you’d be able to tell why this is happening after completing this guide. Follow the necessary steps to turn it off once you’ve identified the reason behind it. Comment below if you have any questions about why your check engine light is on even after changing the MAF sensor.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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