Mass Airflow Sensors Control The Air-Fuel Mixture In A Vehicle's Engine

Mass Airflow Sensors Control The Air-Fuel Mixture In A Vehicle’s Engine

A sluggish MAF sensor that is slow to react to changes in airflow can cause a variety of drivability and emission problems.

mass-airflow-sensor

One of the many things an engine management system has to know before it can accurately control the air/fuel mixture and spark timing is how much air is entering the engine. More air needs more fuel, as does more load on the engine and a wider throttle opening. The Throttle Position Sensor (TPS) can tell the PCM if the throttle is closed, part open or wide open, and the Manifold Absolute Pressure (MAP) sensor can measure intake vacuum as an indicator of engine load.

On fuel-injected engines with “speed-density” engine management systems, the Powertrain Control Module (PCM) can estimate airflow using these inputs, plus air temperature and engine RPM. But it’s not as precise as what can be achieved with a Mass Airflow (MAF) sensor. That’s why MAF sensors are used on a majority of late-model, fuel-injected engines.

Most fuel-injected engines use a Mass Airflow Sensor to obtain a more precise measurement of airflow. The MAF sensor is located in the tubing between the air filter housing and throttle. The sensor measures airflow with a heated element that is cooled by air flowing past the sensor. The amount of cooling the element experiences is directly proportional to airflow, so the PCM can get a very accurate reading on how much air is actually entering the engine. The sensor produces a digital frequency signal that changes with airflow.

Several things can upset the accuracy of the MAF sensor readings. Any air or vacuum leaks downstream of the sensor can allow “unmetered” air to enter the engine. This includes loose fittings or clamps in the plumbing between the air filter housing and throttle, as well as any vacuum leaks at the throttle body, intake manifold or vacuum hose connections to the engine.

Anything that contaminates the surface of the sensor also can screw up its ability to respond quickly and accurately to changes in airflow. This includes fuel varnish and dirt deposits as well as any debris that might get past of flake off the air filter itself. Some aftermarket “high-performance” air filters that use an open cotton weave filter element have been know to cause such problems.

A sluggish MAF sensor that is slow to react to changes in airflow can cause a variety of drivability and emission problems. The engine may start and stall or be hard to start, it may hesitate or stumble when accelerating or when the engine is under load, it may idle rough and get poor fuel economy.

Depending on the circumstances, the PCM may or may not detect the fault, turn on the Check Engine light and set one or more fuel mixture or sensor-related codes. So, the first step in diagnosing a suspected MAF problem is to hook up a scan tool to the vehicle and check for codes. The second step would be to look at the MAF sensor readings and fuel trim to see if the sensor is generating a good signal and that the engine management system is responding appropriately.

If a sensor has failed, there will be no signal. Sometimes the issue is in the sensor’s wiring circuit. A loose or corroded connector, broken or shorted wire may be causing a communication problem. That’s why its important to check the wiring circuit to make sure there are no problems there before replacing the sensor.

If the wiring checks out okay but the sensor seems to be under-reporting airflow or is sluggish, the sensor element is probably dirty and needs to be cleaned. Using an aerosol electronics cleaner or a product designed specifically to clean dirty MAF sensors will often restore normal operation and save your customer the expense of replacing the sensor. No other type of cleaner should be used to clean a MAF sensor because the wrong type of cleaner may contaminate or damage the sensor element.

You May Also Like

Advance Launches ‘Diehards Choose DieHard’ Campaign

The campaign features former Marine sergeant and world-renowned climber Kirstie Ennis.

Advance Auto Parts has unveiled a 60-second documentary-style video and campaign featuring former Marine sergeant and world-renowned climber Kirstie Ennis.

Titled “The Climber,” the video chronicles Ennis’s journey from serving in the U.S. Marine Corps and the loss of her leg above the knee after her helicopter went down in Afghanistan. It also captures her recovery and focus on tackling the Seven Summits, the highest mountain in each of the seven continents.

MEMA Establishes Center for Sustainability

The mission of the new Sustainability Center is to serve MEMA members wherever they are in their sustainability journey.

MEMA Names Jackson Executive Director of Strategy and Research

He most recently was executive director of strategy and research for MEMA’s light-duty original equipment division. 

MEMA Taps Gardner to Lead Marketing and Communications

Prior to MEMA’s reorganization, marketing and communication responsibilities were siloed across MEMA’s four divisions.

MEMA Reveals New Business Structure, Branding Strategy

MEMA will operate with two groups: MEMA Aftermarket Suppliers and MEMA Original Equipment Suppliers.

Other Posts

Schaeffler Releases Technical Bulletins for LuK Product Line

For more than 50 years, LuK has been one of the most trusted and recognized brands in the automotive aftermarket.

NPW Holds 32nd-Annual Charity Golf Tournament

More than 100 players received tips from PGA’s Erik Compton during the event.

Auto-Wares Recognizes Valvoline as Supplier of the Year

Auto-Wares presented eight awards at its Winter Live Sales Meeting in Grand Rapids, Michigan.

ASE Announces 2022 Award Winners

“We had a tremendous group of nominees, and they all were deserving of this recognition,” ASE CEO Tim Zilke said.