Is your engine struggling to accelerate, failing to start, or getting less gas mileage lately? A bad Mass Air Flow (MAF) sensor may be the cause. The MAF sensor is an important engine management component and measures the air entering your engine, optimizing performance.
Let’s examine the typical symptoms of a failing mass air flow sensor and what it could cost to replace the MAF sensor.
What Is A MAF Sensor?
A mass air flow sensor, or air meter, is a key component of your vehicle. More specifically, it measures the air entering the internal combustion engine (mass flow of air).
Based on these inputs, the engine control unit uses the variable values from the MAF sensor to determine the mass of fuel to be injected to keep a balance, or give and take the ratio of air and fuel (in gasoline combustion engines).
Note that air density is not constant; it is affected by temperature, pressure, humidity, etc. This is yet another instance where MAF sensors help, since they are more accurate than volumetric flow sensors when it comes to measuring the intake air quantity into each cylinder.
How Mass Air Flow Sensors Work
The MAF (Mass Air Flow) sensor in your car is integral to engine performance. It tells your car’s computer how much air is entering the engine at a given moment.
Knowing the exact airflow helps the computer determine how much fuel to inject for maximum combustion efficiency.
Types of MAF Sensors
Hot Wire MAF Sensors
These are the most common and use a hot wire or film element suspended in the airflow. As air flows past the heated element, it will cool down the heated element.
The MAF sensor measures how much electrical power is required to maintain the temperature of the wire, and the wire will require more power as more airflow passes. The MAF sensor provides the car’s computer with a precise measure of airflow into the engine.
Hot Film MAF Sensors
These sensors work similarly to hot wire sensors but use a heated film, rather than a heated wire. The film is generally more durable and less prone to contamination. Hot film MAF sensors will also provide better readings over a wider range of air temperatures.
How do they work
Based on this calculation, the computer then adjusts the fuel injection based on the airflow information given to maintain the ideal air-fuel ratio.
Air enters your car’s intake system and passes through the MAF sensor.
This process can be summarized in detail.
- The digital signal is used by the car’s computer to calculate the mass of air flowing into the engine.
- The MAF sensor heated element (wire or film) is held to a constant temperature that is above the temperature of the incoming air.
- As the intake air passes the heated element, it starts to cool the heated element.
- The MAF sensor monitors the electrical current necessary to maintain the sensor element at a constant temperature.
- The electrical current is translated into a digital signal.
Symptoms of a Bad MAF Sensor
Your mass air flow sensor is the “eyes” and “ears” of your engine’s computer; it provides the exact rate air is flowing into the combustion chambers. When the MAF sensor begins to report bad data, you can encounter all kinds of problems under the hood.
Without good readings, your engine’s computer isn’t sure how much fuel to add, and the delicate balance is ruined. Below are the most common MAF sensor warning signs, from most frequent to least serious:
#1. Check Engine Light.
Usually, the first warning sign that a MAF sensor is bad is your check engine light. This light may come on for many reasons, but it’s worth investigating further, as you may discover the MAF sensor is the source!
Your vehicle’s engine control module (ECM) will constantly gather readings from your MAF sensor. When the sensor’s readings are outside of normal parameters, it stores a trouble code in memory that will trigger the check engine light.
Common MAF-related codes are P0100, P0101, P0102, P0103 and P0104. Again, the check engine light can mean many things, but if you also notice other symptoms, this can help to narrow down the fault.
Driving a Volkswagen, Audi or any VAG vehicle, you’re likely to see an EPC light displayed in your dash.
#2. Poor Engine Performance.
If the MAF sensor is faulty, your engine’s performance will likely suffer. The car may feel slow, unresponsive, and likely struggle, hesitate, or stumble when pressing on the accelerator.
That’s because the engine computer is getting bad airflow readings, which means it can not provide the proper fuel.
The issue can sometimes be even worse under hard acceleration (like merging onto the highway) or climbing hills. It can be hard to find the correct air-fuel mixtures when heavy acceleration is required.
#3. Rough Idling.
One of the first signs you will notice when your MAF sensor is failing is when you are not moving. All of a sudden, your engine is bouncing up and down at idle or the tachometer is flying back and forth with no reason.
This is because your engine computer is essentially flying blind! It does not have decent airflow data and cannot keep a steady idle.
Keeping an eye on your tachometer at lights or in park, if the needle is bouncing between 500 and 1000 RPM instead of holding steady around 600 RPM or if the engine, as you feel it, is shaking or vibrating more than usual, could also mean the MAF sensor is faulty.
#4. Bad Fuel Economy.
Have you noticed a decrease in your fuel economy? A bad MAF sensor could be a reason. In the event the MAF is sending bad data to the computer, it usually responds by adding more fuel into the engine (aka: running rich).
This is considered a safety measure to avoid engine damage, but it can seriously impact your economy. You might even experience a drop in the number of miles per gallon you are getting by 10-20% (or more!) under normal driving conditions.
This effect can be noticed while highway driving, as you normally would get the best fuel efficiency, and if you think you have a bad MAF sensor, a long-distance road trip is likely the last thing you want to do.
#5. Engine Stalling.
A faulty MAF sensor can cause your engine to suddenly die. This will usually happen at the most inconvenient time, like when stopping at a light or pulling away from a stop. This is caused when your engine is getting either too much or too little fuel due to the improper amount of air readings being taken by the MAF.
Sometimes you will be able to start the engine again right away, but only to have the same issue randomly reappear. Some drivers report stalling is worse when the engine is cold or when it is humid out.
If your vehicle is starting to stall, especially coupled with some of the previous symptoms such as rough idle, this cause needs to be addressed right away so you do not get stranded somewhere.
#6. Black Exhaust Smoke.
MAF sensor failure often has your engine running rich, as in too much fuel for how much air, and one clear indication of this is dark Gray or black smoke coming out of your exhaust when you accelerate.
This is because excess fuel enters your combustion chamber and does not burn completely. You may also smell heavy gasoline fumes coming from your exhaust, along with the black exhaust. This symptom is usually more prominent in newer cars that typically run very clean.
Your car’s ECM may store fuel trim Diagnostic Trouble Codes, like P0170 and P0173, in addition to MAF sensor-related DTCs. An OBD2 scanner will confirm.
#7. Hard Starting.
A bad MAF sensor can make starting your car harder than normal, especially with a warm engine. You may find that you need to crank your engine longer before it starts, or you may need to start it several times before it runs.
This is because the incorrect air measurements result in the engine being supplied incorrect amounts of fuel while starting, and you may notice that you need to hold the gas pedal down slightly while starting it (something that you may never have had to do until now).
#8. Engine Surges While Driving.
A failing MAF sensor may cause your car to unexpectedly surge, jerk, or buck when you drive at a consistent speed on the highway. It feels like someone is pushing down on the gas pedal and letting up, even if your foot is steady.
Since the MAF sensor is sending erratic signals about incoming air, your engine’s computer is constantly adjusting the fuel mixture to match the incoming air. Surging is most notable when driving on flat roads while trying to maintain a constant speed.
#9. Failed Emissions Test.
If your area has emissions testing, then a failed emissions test is a good probability with a faulty FAF sensor. Anytime you have an air-fuel ratio that is off, your engine will produce higher levels of pollutants than the state inspection requirements allow.
Modern cars typically have emissions trouble codes stored as a characteristic of an abnormal measurement that they cannot fully control, and will automatically fail on emissions testing.
Even if your car is running okay at the moment, if your MAF Sensor is not working as it should be, you may still fail emissions testing.
Reasons for MAF Sensor Failure
A mass airflow sensor can fail for any number of reasons. These reasons include engine debris, electrical issues, age, dirt or blockage in a filter, air leaks, and contaminants like oil.
Contamination and Dirt Build-up
Dirt and contaminants in your engine will lead to trouble, and this can be especially true when we are referencing the MAF sensor and the interior of your engine. If you do not have somebody clean it and tune it up, it will likely fail.
Dirty filters are one of the more typical reasons, and we always suggest having your filter replaced once a year.
Electrical Issues
Electrical and connection issues can be a cause for trouble with your mass airflow sensor as well as your motor. If the connection is corroded, old, and damaged, it is time to have a certified installer take care of that as soon as possible.
Sensor Damage from Extreme Conditions
A common issue for mass airflow sensor failure for Hyundai vehicles is the exposure of under-hood components to the elements. Extreme cold or even extreme weather can lead to a mass airflow sensor failure.
Extreme moisture and extreme heat can lead to similar failures, so be mindful of bad weather and parking for long periods.
To Clean, Repair, or Replace?
Diagnosing the problem is the first step, but what is the remedy? The remedy will depend upon the amount of damage. Let’s consider the options:
Cleaning the MAF Sensor
In general, MAF sensor problems can usually be cleaned rather than repaired or replaced, provided that it is not physically damaged. A good cleaning can remove dirt, oil residue, and debris that could affect the sensor’s performance. Here’s how to clean the sensor:
- Use the Correct Cleaner – Don’t ever use carb cleaner, brake cleaner, or other harsh solvents as they can damage the sensor. You will want to use only a dedicated MAF sensor cleaner spray. Follow the MAF sensor cleaner manufacturer’s instructions exactly for best results.
- Remove & Spray the Sensor – After you have unplugged and safely removed the sensor, spray 10-15 bursts of cleaner around the inside of the sensor, including the hot wire or hot wire plate. You will want to clean all sides of the part, housing, connectors, and terminals.
- Allow the Sensor to Dry – Allow the sensor to air dry for several seconds before reinstalling. Do not touch the sensor elements with your fingers or any tools. After you reinstall the sensor, wait a few minutes before restarting the vehicle.
Repairing the MAF Sensor
If cleaning does not resolve the issue or the MAF sensor is physically damaged, the repair option may be an option. We need to note that the repair option is often not a valid option, as the internal components of the MAF sensor, including the very small wires, may be easily damaged.
There are certain scenarios that may allow for a repair option or modifications, for instance, if you have damaged wiring harnesses or damaged connectors that are part of the MAF sensor, which would ease the repair process.
Replacing the MAF Sensor
In situations when the cleaning or repair option does not work, your best option is to run with the replacement option.
The question then is, how do I know if the MAF sensor is faulty and requires replacing?
- Any signs of cracked sensor housings or damaged internal components?
- If the problems continue, and you have comprehensively cleaned the MAF on multiple occasions.
- If you have tried a variety of aftermarket cleaning options and none appear to resolve the issue.
The MAF replacement option is fairly simple to conduct. In the case you have not located the MAF sensor yet, it should be located between the air filter and the intake, although the location may vary for each vehicle. Consult a repair manual for your vehicle or an online source, if needed.
- Disconnect the negative terminal of the vehicle’s battery as a precaution against electrical shock or starting the vehicle accidentally.
- Verify you have the appropriate tools, including a socket set, screw drivers, torque wrench, safety apparel and code reader, in addition to the new MAF sensor.
- Remove screws or clips from the old sensor, and carefully pull the old MAF sensor out of position.
- Next, carefully seat and secure the new MAF sensor into position, without touching the sensor elements.
- Reconnect the electrical connectors.
- Finally, clear the ECU clear fault codes and reset it with your code reader.
Cost of Replacing MAF Sensor
The cost of replacing a mass air flow sensor will vary according to the particular make/model of your vehicle and whether you go OEM versus an aftermarket product.
Cost of Parts
- OEM MAF sensors typically range from $150 to $400.
- Quality aftermarket MAF sensors range from $70 to $300.
- Basic (or lower quality) aftermarket MAF sensors start from around $30.
NOTE: While going with an aftermarket sensor can save money, certain cars can be sensitive to a non-OEM part in regards to the MAF sensor. If you aren’t completely sure what route to take, asking a mechanic or parts specialist is a good idea.
Cost of Labour
- A professional mechanic would expect to charge anywhere from $50 to $100 for installation, and the job will take somewhere between 10-60 minutes. Some luxury or European cars may take longer because of complicated intake systems or difficult-to-access locations.
- Most places don’t charge by the minute, so many have a 1-hour minimum; with this in mind, the prices can easily fall into the $120 to $150 range.
- If the shop you normally go to follows this standard business model, you would probably be better off going somewhere else to have this job done.