How To Tell If Your Mass Air Flow Sensor Is Bad

The mass air flow (MAF) sensor, part of your vehicle’s electronic fuel injection system, is responsible for calculating the total amount of air entering the engine. A faulty MAF sensor can cause your vehicle to run too rich or run too lean. You’ll notice if the tailpipes eject black smoke or when the engine runs rough or backfires. You may also notice you’re filling up at the gas station more than usual.

How the MAF sensor works

MAF sensors are located between the air filter and the throttle body and are responsible for measuring the amount of air entering the engine.

Most vehicles have a hot wire MAF sensor. It has one heated wire and one ambient temperature wire. The microprocessor inside the MAF sensor measures the air entering the engine by maintaining the temperature of the hot wire 200°F above the ambient incoming air. The energy required to maintain the sensor at the same temperature is calculated and sent to the powertrain control module (PCM). The PCM then controls the injectors to deliver the specific amount of fuel that’s proportional to the airflow, creating an air fuel mixture that, ideally, is perfect for your engine.



A bad MAF sensor can cause your vehicle to experience poor drivability issues such as engine stalling, jerking or hesitation during acceleration. This could happen while speeding up on the highway on-ramp or cruising down a city street. These issues can create dangerous situations causing accidents and injury. If you experience any of these symptoms you should examine your vehicle as soon as possible.


Your vehicle needs the proper ratio of fuel to air in each combustion cylinder. Running rich means there is too much fuel and not enough air. Signs that your vehicle is running rich include:

  • Black smoke exiting the tailpipe
  • Worse fuel efficiency than usual
  • Rough idling
  • Check Engine Light

These issues can happen when the MAF sensor is damaged or when its wires are coated with dirt. It can’t measure airflow accurately, therefore sending incorrect information to the PCM. When it overestimates the airflow, the PCM releases too much fuel. Most of the time, you or a mechanic can fix the problem by cleaning the MAF sensor’s wires. If you’re noticing a Check Engine Light. Stop into AutoZone to have the code read for free with Fix Finder.


Running lean is the opposite of running rich. It means your vehicle has too little fuel and too much air. Similar to running rich, the MAF sensor is sending inaccurate information to the PCM. This time underestimating the amount of airflow instead of overestimating it.

Although this will temporarily improve your fuel efficiency, running lean for too long can seriously damage your vehicle. You may experience:

  • Engine hesitation and/or surging
  • Hard engine seizures
  • Hard starting
  • Check Engine Light

As with other MAF sensor problems, the solution may be as simple as cleaning the wires. However, it’s also a good idea to have a mechanic check your vehicle for damage.


If your Check Engine Light is on, use a code reader to see what diagnostic trouble codes the system puts your way. If you don’t have a code reader, stop by AutoZone to use our free Fix Finder program.

This Code’s full read out is: P0101 – Mass Air Flow Sensor Circuit Range/Performance.

The engine computer uses the MAF sensor signal to determine how much fuel needs to be injected to meet the proper air-fuel ratio. The MAF sensor signal is also used to calculate engine load, meaning it can cause trouble for the traction control system, or change the automatic shifting pattern in applicable vehicles. This code is most commonly caused by a dirty, obstructed, or faulty MAF sensor, but can also be caused by issues including:

  • Damage to the intake boot
  • Vacuum leaks
  • Clogged or improperly installed engine air filter
  • Clogged-up cat converter or restricted exhaust

Because there are other potential causes besides the bad MAF sensor, it’s worth looking into these other possibilities so you are positive this code is being caused by the sensor before you go about replacing it.

Common Check Engine Light Causes: MAF Sensor

A malfunctioning MAF sensor may cause your vehicle to jerk during acceleration, run too rich, or run too lean. Make sure to fix the problem right away so you can be safe, avoid costly repairs, save money at the pump, and avoid being stranded on the road. Be sure to take a look at the mass air flow sensor before replacing it, you may only need to clean your MAF. Stop by your local AutoZone for advice on symptoms of a bad MAF sensor.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

FREE Loan-A-Tool® program requires returnable deposit. Please note that the tool that you receive after placing an online order may be in a used but operable condition due to the nature of the Loan-A-Tool® program.

Related Posts