A Mass Air Flow Sensor measures the amount of air flowing into the engine. The engine control module or engine control unit (ECM) uses this information to manage the Air-Fuel-Ratio or AFR. A bad MAF feeding incorrect information can cause all kinds of issues. The AFR may be too lean, leading to hesitation, poor acceleration, and difficulty starting when the air mass fuel ratio is incorrect. Keep reading to learn the top bad MAF sensor symptoms.
If the AFR is too rich, there is too much fuel entering the system, leading to an increase in fuel consumption, potentially causing the engine to produce black smoke exiting the exhaust system, engine running roughly, surging, and hesitation of the engine. Change the air filter and clean the MAF to ensure they are not limiting the flow of air into the engine. Clean filters maintain the air and fuel mixture at an optimum level.
10 Symptoms of a Bad Mass Air Flow Sensor
There are at least ten common symptoms that can indicate the MAF sensor is bad. However, before replacing the MAF, car owners should check for all of these symptoms and diagnose the actual cause. We will expand on each of these later in this post.
- Check Engine Light Comes On
- Trouble Accelerating
- Rough Idle
- Poor Fuel Economy
- Black Exhaust Smoke
- Hesitation or Surging
- Hard Starting
- Difficulty to Turn Over
- Engine Stalls
- Clogged Air Filter
Check Engine Light Comes On
The ECM can cause the check engine light on the dash to illuminate whenever there is a malfunction. The ECM also stores diagnostic trouble codes, which can be read by a mechanic with a code reader. The code can indicate a bad MAF as well as other codes. This code and some of the following symptoms can assist your mechanic in narrowing down the specific problem.
Poor or a delay in acceleration suggests that the air-fuel ratio is off. The fuel is not fully combusting and therefore delivering insufficient power to the engine to drive acceleration. The MAF may not be accurately reporting the airflow. Acceleration hesitation or engine drags can also be caused by several other conditions or malfunctions, including clogged fuel lines and fuel injection devices or a clogged fuel pump impacting internal combustion in the engine.
An engine runs smoothly when the engine receives the correct fuel to air mixture, and all sensors are delivering information to the ECM. Anytime a sensor provides poor information, such as an incorrect airflow reading, the ECM will try to compensate by adding more fuel or lowering the fuel inserted into the combustion chamber.
As the airflow changes from lean idling to too much fuel, so does the engine, causing the RPM to fluctuate and run rough. Overall, smooth idling is difficult to achieve without the proper amount of fuel.
Poor Fuel Economy
The ECM will attempt to compensate for the airflow readings from the MAF, adding more fuel to the combustion chamber than needed. With insufficient air, the fuel does not completely burn, increasing pollution levels and causing a lower fuel economy. As soon as drivers notice the engine using more fuel than normal, have a mechanic check for error codes and the condition of the MAF.
Black Exhaust Smoke
In some situations, the ECM may compensate by attempting to add more fuel than needed when more power is required, and there is insufficient airflow indicated by the MAF to the ECM. The excess fuel does not fully burn, causing black sooty smoke to exit from the exhaust pipe. Drivers allowing this condition to persist risk clogging the catalytic converter, which can be expensive to replace.
Hesitation Or Surging
As the ECM attempts to compensate for erratic data from the MAF, it may cause too much fuel to enter the combustion chamber or too little. As more fuel is added, your car may surge ahead with extra power as if you are accelerating. If insufficient fuel is added, there may be some hesitation. Both situations can be unnerving, especially if you are in heavy close traffic.
The ECM depends on readings from the MAF to determine how much fuel to add while the car’s engine is running. Also while attempting to start the engine. The ECM adds more fuel to start the engine and keep it running until the engine reaches normal operating temperature. You may find the engine difficult to start, or it may not run well, especially while the engine is still warming up.
Difficulty To Turn Over
The engine may be difficult to start or won’t start at all if the MAF is not reporting accurate information to the ECM. The fuel supplied to the engine may be insufficient to start the engine because too lean a mixture of fuel and air is provided to the engine cylinders. Without the assist of cylinders firing, the engine will be difficult to start. Avoid running the starter for too long since it will overheat and drain your battery quickly.
Engines can stall for several reasons; however, one of the main reasons is too lean a fuel to air mixture. The ECM depends on the MAF to tell it how much air is entering the system. If the fuel to air mixture is very lean, the engine may stall under load. This situation can be dangerous if the engine stalls while driving or at a busy intersection.
Clogged Air Filter
The MAF could be operating as designed, but insufficient air is entering the system, causing the ECM to increase the fuel mixture to deliver more power. The culprit can sometimes be a clogged air filter and is one of the simplest things to check before heading off to a mechanic for repairs. Replace the air filter if you notice dirt and debris, especially insects clogging the filter.
What Does A Mass Airflow Sensor Measures?
Located between the throttle body and the air filter, the MAF measures the airflow into the engine, which varies due to temperature and local pressure. The measurement is reported to the ECM, which calculates the fuel to be delivered to the injectors. The intake air temperature sensor also reports the temperature of the air.
How to Fix a Bad MAF Sensor
Before replacing the MAF sensor, car owners may want to check the air filter is clean. Also, check that the wiring to the MAF is secure. If your check engine light is on, grab a scanner and read the error code that causes the light to illuminate. The scanner will have a list of common trouble codes for your vehicle. Code Po101 – MAF suggests there is a problem with the MAF. However, the code is generated sometimes due to:
- Intake Boot Damage
- Vacuum leaks
- Clogged air filter
- Clogged catalytic converter or plugged exhaust system.
Can You Clean a Dirty Mass Airflow Sensor?
The MAF sensor can be cleaned. Some manufacturers recommend sensor cleaning every time the air filter is replaced. Use a recommended cleaner for dirty MAF’s, spray 10 or 15 sprays onto the sensor wires and plate while being careful to avoid damaging these items. Cleaning the MAF is relatively quick, easy, and inexpensive.
How Much Does It Cost to Replace a MAF Sensor?
If you do the work yourself, replacing the faulty mass airflow sensor may cost in the range of $300 depending on the make, model, and year of the car. A mechanic can replace mass airflow sensors; however, their time and profit may push the MAF sensor replacement cost closer to $500 or more for the service.
Bad MAF Sensor Symptoms Summary
The MAF measures the airflow into the engine assisting the ECM to control the fuel to air mixture. Regular cleaning of the MAF and replacement of the air filter can help to avoid future problems.
Having a faulty mass air flow sensor or oxygen sensor can result in excessive fuel consumption. The mechanic can try to clean the sensor before getting it replaced, and this can save you money. Also, he/she can use various scan tools to determine if your vehicle needs other repairs.
Sometimes the check engine light illuminates for clues regarding why your engine may be surging, hesitating, hard to start, black smoke coming from the exhaust, or lacks power. The diagnostics of a bad (MAF) mass air flow sensor and replacement should be left in the hand of a professional.