All fuel injected engines need a mass airflow sensor to meter how much air the intake manifold is pumping into the engine. The car’s powertrain control module (PCM) then uses this data to determine how much fuel to inject for perfect combustion.
What is a Mass Airflow Sensor (MAF)?
A MAF is a fine sensitive sensor that uses air flowrate and intake channel diameter to calculate the volume of air going past. In a closed system without a vacuum leak, the mass airflow sensor can give the PCM a very accurate estimation of how much volume of air gets into the engine.
There are different types of mass airflow sensors. The most common in modern cars are the hot wire airflow sensors.
- The sensor has one or more electrically heated wires (hot wires)
- A temperature sensor sits close to the wires
- Low air flow doesn’t blow away much of the heated air while higher air flow blows away more heat cooling up the wire
- The system compensates for the heat loss by passing more current through the hot wire to retain the temperature
- The amount of current going through the wire to sustain the temperature is proportional to air flow
Signs That You Have a Bad Mass Air Flow Sensor
Since the MAF plays a critical role in managing your powertrain, any problems from it will give noticeable engine problems. Here are the most common issues to look out for.
Note that they might also hint at other problems in your powertrain. The only way to confirm your MAF is the problem is by bench testing it or eliminating other possible culprits.
Your Check Engine Light Pops Up
Whenever the readings from your MAF deviate from the normal, your PCM will detect the problem and store an error code. This ill in turn illuminate the Check Engine Light on the dash. You’ll then need a scan tool to pull the recorded trouble codes.
The trouble codes to expect include:
- P0101: MAF circuit malfunction
- P0101: MAF circuit range/performance problem
- P0102: MAF circuit low
- P0103: MAF circuit high
- P0104: MAF circuit intermittent
Apart from these mass airflow sensor-specific codes, your engine could also throw lean or rich error codes since the PCM doesn’t have all the information it needs to create the perfect air to fuel ratio.
The Engine Idles Rough
An engine only idles smooth if a couple of things are right. While engine mounts play a critical role in smoothing out vibrations from your engine, they will be overwhelmed if you have a rough idle.
The engine shakes and surges in a way you can feel in the cabin. The vibrations are because without the proper air-fuel mix, the engine won’t run smooth or produce enough power to keep things powered at low idle RPM.
The rough idle could either be randomly surging RPM or a hard-to-miss vibration and rattle in the cabin.
Trouble Accelerating
Sometimes, your MAF might not be completely damaged. In this case, it will still work within acceptable tolerances. Despite not throwing an error code, it will still impair your engine’s performance.
You will have trouble accelerating to speed and your engine will feel sluggish. In some times, your engine will hesitate or surge. For instance, you will get a less than expected response when you press the accelerator pedal or get erratic surges in power without changing the throttle body position.
Poor Fuel Economy
Your mass airflow sensor doesn’t have to fail fully to affect your fuel economy. In cases where its shortcomings cause the engine to run rich, you will burn more fuel than necessary.
The result is poor fuel economy.
Your Engine is Hard to Start
Starting an engine and running it until it warms up requires more fuel than maintaining it at idle. Getting the mix right when cranking ensures that your car comes to life as fast as possible.
A faulty MAF makes it hard to attain this mix. You might have to crank your car longer or a couple of times before it turns over.
Black Exhaust Smoke
The last problem to look for that could hint at a faulty MAF is too much black exhaust smoke. This happens if the engine is running too rich. The extra smoke means more emissions for the catalytic converter.
If you run the engine for days with this symptom without fixing it, chances are your catalytic converter will be ruined. If you’re unlucky, you’ll get the P0420 error code for the catalytic converter is below the threshold.
Newsflash: Catalytic converter replacements aren’t that cheap.
How to Test a Mass Air Flow Sensor
Luckily, you can get all the guesswork out of the way and narrow down all the above symptoms to your MAF. All a mechanic needs is a scan tool and engine specifications.
The scan tool will be set to show mass airflow sensor readings at different engine RPMs. The results will then be compared to known results from a good sensor installed in a similar engine.
If you have a scan tool, plug it into your car and pull up the MAF readings. You can also pull up RPM monitor gauge. Note down the readings at:
- Idle
- 1000RPM
- 2000RPM
- 3000RPM
If your MAF is contaminated, it will show lower airflow readings per RPM than a known good sensor.
In rare cases, the MAF might show higher airflow readings. This could also hint at a problem
Pro Tip: Ensure that you are comparing the MAF readings to those of a good sensor from a similar engine. A 2000cc engine will have different readings from a 3000cc engine even if they’re are installed in the same vehicle model.
While the wrong readings could almost certainly point at a faulty or clogged mass airflow sensor, they could also mean:
- You have a clogged catalytic converter
- There are vacuum leaks somewhere in the system
How to Fix a Bad Mass Air Flow Sensor
MAFs last for very long. Chances are the terrible readings you’re getting are due to dirt and gunk. Here are some things you can do before replacing it:
Shake the Loose Dust and Gunk Off
If you are lucky, some light dust might be all that’s between you and an efficient MAF. Shaking it off might do the trick.
Be keen not to over-stress the wires as they are fine and sensitive.
Use a MAF Cleaner
For a better cleaning impact, consider using a dedicated MAF cleaner. Remember that your MAF is very sensitive. Don’t use the wrong cleaner or be over enthusiastic while at it.
- Remove the mass air flow sensor from its slot in the intake tube
- Spray it with the MAF cleaner. Take care to hold the nozzle clear of the sensor wires
- Let the sensor dry for an hour or two before reinstalling it
Some mistakes to avoid when cleaning the sensor include:
- Don’t use any other cleaner. Brake cleaner, WD40 or any other solvents aren’t perfect. MAF sensor cleaners leave no residue when they dry making them safer
- Don’t clean the sensor while it’s still in the intake tube. This could mess up adjascent electronic systems that read data from the MAF sensor
What to Do After Cleaning or Replacing a Mass Airflow Sensor
After cleaning the sensor, don’t expect the sensor to run perfectly immediately. The ECU has to relearn the new readings from the MAF sensor and recalibrate. Things should get back to perfect after a day or so.
Note that damages to the sensor that leads to new error codes or worse performance won’t fix themselves.
You could accelerate the relearn procedure by resetting all the electronics in your car to default. To do this, you will have to disconnect the car battery terminal for a couple of minutes. 20 minutes is always sufficient.
This will flush all previously learned parameters forcing the car to relearn and recalibrate itself faster.
Replacing the MAF Sensor
In case cleaning doesn’t fix your problem, or you can see visible damage on the sensor, replacing it is the only way out. Ensure that you get the correct OEM or after-market replacement to avoid more problems.
Can You Drive a Car With a Bad Mass Airflow Sensor?
You could keep driving the car but it’s only advisable to do this for a very short distance – preferably to the mechanic’s. Driving long distances with a fouled MAF will not only make your engine less efficient but could also ruin other parts of your engine.
Moreover, your car will get less driveable as the problem escalates. Secondary problems that could crop up include:
Transmission issues when the surging engine puts undue strain on the transmission
- A car that doesn’t turn over or stalls at dangerous places
- A clogged or damaged catalytic converter
- Do I Need to Disconnect the Battery When Changing the MAF?
While you can safely pull out and reinstall the MAF as long as you don’t turn on the car, disconnecting the battery’s negative is always safe practice. It will keep you safe if you accidentally short circuit something or if someone else in the garage accidentally turns on the car.
Additionally, it could be the time you need to reset the car’s computer so that it recalibrates as soon as you drop the cleaned or new MAF sensor back in.