Bad MAF Sensor Symptoms and Causes | How to Clean a MAF Sensor?

The Mass Air Flow Sensor (MAF sensor) plays a crucial role in ensuring the efficient performance of your vehicle’s engine. It calculates the amount of air entering the combustion chamber, enabling the calculation of the accurate air-fuel mixture. This information is then transferred to the powertrain control module (PCM), which controls the fuel injectors’ activity to provide the appropriate amount of fuel. When the MAF sensor becomes faulty, it produces different signs. This article mainly describes the bad MAF sensor symptoms, causes, and how to replace it.

What is an MAF Sensor?

The MAF sensor is a mechanical device that is used to measure the air amount entering the engine cylinder and then transfers this data to the vehicle’s computer (i.e., PCM). The vehicle computer utilizes this data to control the fuel injection rate, ignition timing, and overall engine performance.

 The collaboration of the MAF sensor with the O2 sensor allows for precise control of the engine’s air-fuel ratio.

The O2 sensor complements this process by making adjustments based on variations in the data received from the MAF sensor, thereby further refining the air-fuel mixture.

By providing the PCM (Powertrain Control Module) with precise air flow data, the MAF sensor contributes to the regulation of the air-fuel ratio, fuel injection rate, and overall engine performance.   

Symptoms of a Bad MAF Sensor

When the MAF sensor goes bad, it produces one or more of the following symptoms:

• Check Engine Light illumination 
• Hard Starting
• Misfires
• Black Smoke from Exhaust Pipe
• Rough Idle
• Jerky Acceleration
• Poor Fuel Economy
• Failed Emission Test

1) Check Engine Light illumination 

An illuminated check engine light is one of the clear symptoms of a faulty Mass Air Flow Sensor (MAF). The powertrain control module (PCM) constantly observes the performance of all engine sensors to ensure their proper functioning.

If a sensor, such as the MAF sensor, transmits inaccurate signals to the ECM /PCM, the check engine light is activated.

Thus, when a faulty MAF sensor provides incorrect data to the PCM, the check engine light will be activated. This occurrence is a prevalent sign associated with a malfunctioning MAF sensor.

But it is worth noting that the PCM doesn’t always detect a faulty MAF sensor, meaning that it may remain defective even if the check engine light remains off. To ascertain the presence of any issues, it is advisable to first use an OBD-II scanner to check for diagnostic trouble codes when the check engine light is activated.

2) Hard Starting Conditions

A faulty MAF sensor may lead to hard starting conditions. The ideal airflow mixture supply is compulsory to the engine at the precise moment for a smooth start. If the MAF sensor doesn’t deliver this optimal airflow, your vehicle may be hard to start.

3) Misfires

Misfiring is one of the clear signs of a bad MAF sensor. Your engine misfires when any engine cylinders don’t ignite the fuel properly. To achieve a successful ignition, the engine relies on three key elements:

• Appropriate air-fuel ratio
• Ignition
• Compression

When the fuel-air mixture deviates significantly from the required specifications, it may prevent one or more cylinders from igniting properly, resulting in a misfire. If you encounter any trouble codes related to engine misfiring, it may serve as an indication of a faulty mass air flow sensor.

Read More: Engine Misfire Causes and Symptoms

4) Black Smoke from Exhaust Pipe

The presence of black smoke emanating from your vehicle’s tailpipe is one of the clear signs that the engine is receiving an excessive amount of fuel relative to the air intake.

Consequently, if you observe a significant amount of black smoke, there is a notable risk that the engine is running too rich, and a faulty MAF sensor could be the underlying cause.

In addition, you may observe an increased amount of gray smoke from the exhaust pipe if the engine is running rich. This condition can potentially cause damage to the catalytic converter, a costly component of the vehicle.

Therefore, it is crucial to address this issue promptly to prevent further harm and avoid potential expenses linked to the catalytic converter replacement or repair.

Read More: Causes of Black Smoke From Exhaust

5) Rough Idle

The idling phase of your car’s engine is particularly vulnerable to engine issues. During idle, only a small amount of fuel and air is transferred to the combustion chamber, leaving little room for error which can lead to noticeable issues.

If you experience a very rough idle or if the engine stalls while idling, there is a high probability that your mass air flow sensor is malfunctioning. You need to fix this issue as soon as possible because proper functioning of the mass air flow sensor is very important for maintaining the correct air-fuel ratio during idle.

6) Jerky Acceleration

A defective MAF sensor can lead to various drivability problems, adversely affecting the performance of your vehicle. These issues can be evident as engine stalling, hesitation, or jerking while accelerating. This issue may be particularly hazardous when merging onto highways or driving through city streets.

Such problems can potentially result in accidents and injuries. Therefore, if you experience such issues, it is crucial to promptly inspect your car to address the problem.

7) Poor Fuel Economy

A malfunctioning MAF sensor may result in inaccurate signals being sent to the vehicle computer. In such conditions, your engine may start to run rich and consume more fuel than normal. This, in turn, can result in poor fuel economy.

8) Failed Emission Test

When the MAF sensor fails, it may transmit incorrect information to the PCM regarding the engine load, indicating either a high or low load condition.

To maintain optimal exhaust emissions, your engine relies on receiving a precise amount of air-fuel mixture. However, a bad MAF sensor disrupts this balance, leading to an improper air-fuel ratio and an increase in exhaust emissions.

Causes of a Bad MAF Sensor

• Poor Maintenance: Poor engine maintenance is one of the major reasons of the MAF sensor failure.
• Oil Contamination: If your car contains oiled air filters, there is a high chance for the oil to contaminate the MAF sensor.
• Damage or Wear: Your vehicle’s sensor may wear out with time. This issue usually occurs because of normal wear and tear, but accidents or other damage may also cause mass air flow sensor failure.
• Electrical Issues: The MAF sensor of the vehicle depends on the electrical system to work properly. If there is an issue with the electrical system, such as damaged wiring or a blown fuse, your sensor will be unable to work properly.
• Wrong Installation: If your sensor is not installed properly, it will not work efficiently. This may also be because of wrong installation, using the wrong type of sensor for the car, or not resetting the PCM after repair or installation.
• Contaminants: Contamination is one of the major causes of a faulty MAF sensor. The hot wire of your sensor is very sensitive, and even a very small amount of dirt may force the sensor to measure the wrong readings.

How to Test an MAF Sensor?

• Utilize an OBD-II scanner to access live information from the MAF sensor while the engine is idling. The expected value should be 0 mg.
• Start the vehicle engine and recheck the MAF sensor values. These values must increase as you reverse the engine and decrease when the RPM decreases. If the values don’t change, it indicates a potential issue with the sensor or its wiring.
• Remove the sensor plug and inspect for any signs of rust or corrosion.
• Use the vehicle repair manual to measure the wiring and sensor according to the provided instructions.
• Check the wiring for any signs of damage or corrosion. If any issues are detected, replace the damaged or corroded wiring.
• If a bad MAF sensor is identified, either clean it or replace it, depending on the severity of the issue.
• Clean the MAF sensor using an alcohol or suitable cleaner, ensuring it is thoroughly dried before reinstalling it into the vehicle.

Where is the MAF Sensor Located?

The mass air flow sensor is usually installed in between the intake manifold and the air filter of your engine.

However, the MAF sensor location varies according to the vehicle model or the engine type. Fundamentally, the mass air flow sensor is installed as per the engine design.

MAF Sensor Replacement Cost

The average replacement cost of the MAF sensor varies according to the vehicle model and labor cost. The average replacement cost of the MAF sensor is between $130 and $560. In this cost, the sensor cost is from $80 to $380, while the labor cost is from $50 to $180.

MAF Sensor FAQs

What is the function of the MAF sensor?

The main function of the MAF sensor is to measure the incoming airflow and transmit this data to the PCM, allowing for accurate regulation of the air-fuel ratio, fuel injection rate, and optimal engine performance.

What happens when the MAF sensor goes bad?

When the MAF sensor malfunctions, it can have various negative effects on your car’s engine. The most common symptoms include an illuminated control lamp, diminished engine performance, rough idling, and altered fuel consumption.

Can you drive with a bad mass air flow sensor?

Due to the significant impact a faulty MAF sensor can have on the engine, it is not advisable to continue driving with a malfunctioning sensor. But if your engine is running relatively well, you may drive your car to the local workshop for inspection and repairs.

How can poor electrical connection at the MAF sensor connector impact its performance?

A poor electrical connection at the MAF sensor connector may lead to wrong readings of the sensor. It is essential to carefully inspect the connector terminals and wiring to ensure a proper connection. Additionally, the correct installation of the air filter and proper closure of the air filter box are crucial to stop contaminants from damaging the sensor.

How often does a mass air flow sensor need to be replaced?

There is no specific service schedule for replacing the mass air flow sensor. It is designed to last the entire lifespan of the car unless it becomes faulty. Nonetheless, regular cleaning of the MAF sensor every 110,000 miles can help maintain its functionality and performance.

What to do when a new MAF sensor seems to perform worse than the old one?

The need for sensor replacement may arise due to various reasons, such as issues with the quality of the new sensor or an incorrect diagnosis of the problem. Some manufacturers offer tested MAF sensors to make sure 100 percent accuracy and help prevent such issues.

Can cleaning a MAF sensor fix it?

Inadequate throttle opening caused by a dirty MAF sensor can result in engine stalling or lack of sufficient power. It is important to address cleanliness issues with the MAF sensor to ensure proper engine performance.